Why Japanese and Chinese rules have different Komi? 6,5 and 7,5. Is there any spesific or big reason behind that math ?
Not really. The optimal komi is (probably) 7, but historically there are no draws in Go, so they decided to give half a point to white in the Chinese rules, and half a point to black in the Japanese rules.
A little better explanation: it used to be 5.5 in both rulesets, but this appeared to be not high enough. Therefore it was raised a minimal amount in both rulesets. Since in Chinese scoring the score is always odd (assuming no points being lost in seki) a komi of 6.5 would be the same as a komi of 5.5, thus they made it 7.5 instead.
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Wow! That’s possibly the best summary of the situation I’ve ever read! Kudos @Vsotvep <3
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Everything you want to know about this subject, can likely be found here: Sensei’s Library - Komi. For the sake of answering you directly, I will quote a few bits of this article below.
Komi
In a game of Go, Black has the advantage of first move. In order to compensate for this, White can be given an agreed, set number of points before starting the game. These points are called komi.
A typical value for komi is in the region of 5-8 points, but numerous different values have been used in practice. To prevent a drawn game in the case of jigo, the komi is commonly set to a fractional value such as 6.5.
Territory scoring
Today the standard komi in Japan is 6.5 points, introduced September 2002.[1] The Honinbo tournament used a komi of 4.5 points in 1939, changing to 5.5 komi in 1973. The Meijin tournament used a komi of effectively 5.5 (5 points with White winning jigo). Korea also switched from 5.5 to 6.5,[2] as have most western countries that use territory scoring.
Area scoring
The usual komi in China was formerly equal to the 5.5 used in Japan, but was changed to 7.5. The jump is two points, because under area scoring the score is almost always odd.[3] The Ing rules also have a komi of 7.5, specified as 8 points with Black winning jigo. The American Go Association have also changed komi from 5.5 to 7.5 in August 2004, effective 2005. The New Zealand rules specify a komi of 7.
History of Komi
Although there were some games played with compensation in the 19th century, more substantial experiments came in the first half of the 20th century. Several values were experimented with, until a value of 4.5 became the standard from the 1940’s onward. Game results from the next two decades showed that 4.5 komi still favored black, so a change was made to 5.5 komi, which was mostly used for the rest of the century in both Japan and China. At the start of the 21st century, the komi was increased yet again, to 6.5 in Korea and Japan and to 7.5 in China.
The Correct Komi
In theory, the perfect komi for a given ruleset is a well-defined concept: it is the number of points by which Black would win given optimal play by both sides. Due to the absence of perfect players this number cannot be determined with certainty…
Statistical Komi Analysis
Because it is as yet impossible to determine perfect play, statistical analysis has been used to judge whether a given value of komi is fair or not.
Fair komi
Of course there needs to be made a distinction between perfect komi as defined above and fair komi, which can be defined as that komi that gives a person against an evenly matched opponent a winning percentage that is as close to 50 percent as possible (treating a draw as half a win and half a loss).
Perfect komi stays constant, but as insights change over time, fair komi can change with them, possibly even becoming fractional despite the used ruleset if the statistics can justify it. It is likely, though, that the historical 5.5 komi is an artifact of tradition and imperfect knowledge (and a desire to avoid jigo) rather than an insight different from today.
I hope this helps 
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Thanks for that information 
wow, sensei Library. This is Big Help For Me. Thank You
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You are very welcome 
. I’m not sure if you are new to Go, but if you are, you might be interested in some resources I’ve put together for new players:
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Why Japanese and Chinese rules have different Komi? 6,5 and 7,5. Is there any spesific or big reason behind that math ?
Yes. Imagine a game after one move. Black owns the whole board at that point. If the game ended after that move, Under Japanese rules black would have 360 points, under Chinese rules, black would have 361 points.
Now image playing 3x3 Go. Assuming perfect play using Japanese rules, Black will end the game with 8 points, under Chinese rules, black will end the game with 9 points.
Hence, in Chinese rules, komi is one point higher than it is in Japanese rules.
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That’s an interesting hypothesis, but I’m not sure if the history supports that assertion.
Not too long ago, komi under both Japanese and Chinese rules was 5.5 points, but I think people came to realize that still favored black slightly. Hence, a few decades ago, komi was increased by one point to 6.5 for Japanese rules.
However, under Chinese rules, the vast majority of games end with a score difference that is an odd number. Hence, moving from 5.5 points to 6.5 points would not make a substantial difference. Hence, they jumped by 2 points to 7.5, in order to actually make a difference.
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Another perspective on how Komi has changed over time. From the New Zealand Go Society’s website: History of New Zealand Rules of Go
A komi of 5.5 was in use in 1985 and New Zealand tournaments consistently gave a higher percentage of games won by black. When we changed to Chinese style rules this increased as black gets a slight advantage over Japanese-style rules. The komi was increased to 6 in 1986. Later the komi was increased again to 7.
Besides trying to even out the advantage of black playing first it was felt that perfect play should give a draw. Also we felt that some draws in tournaments were a good thing for the conduct of the tournament (requiring fewer tiebreaks). Probably a komi of 9 would be nearer the correct value but we are still a little conservative.
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Bet they’re glad they didn’t go to 9 now haha
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Why do you say that?
For what it’s worth, not only is there any need for Komi on 3x3 boards, with perfect play, White cannot win on the 3x3, 4x4, 5x5, or 6x6. From Small Board Go:
Go has been solved[1] for boards up to and including 6x7 with area scoring (Ref. Mini-Go by Ted Drange with assistance from Bill Spight). With ideal play (and no komi), Black wins 3x3 by 9, 4x4 by 2, 5x5 by 25, and 6x6 by 4.
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Because AI have shown that 7.5 gives an advantage to white, leaving a very strong argument that 7 is probably the best komi
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I hadn’t heard that. Any chance you know of a source where I could read more about this? I find the topic extremely interested 
Observe: the power of tengen
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HAHA, so true 
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With AI being so new, I don’t think there have been any conclusive studies done yet… but all the AI trained on 7.5 komi give white a move 0 winrate of something in the area of 55%
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Those win points assume Chinese scoring, in all known cases, assuming perfect play, Black’s score is one point less in Japanese scoring.
That would change the values to:
3x3 by 8
4x4 by 1
5x5 by 24
6x6 by 3
Meaning White still walks away with a victory. However, I don’t think it is possible for Black to win by only 24 points on a 5x5 
If you are using Japanese scoring, it isn’t possible for Black to win by any more than 24 points (again, assuming perfect play because the game is solved after all.) In order for black to score any points at all, they must play a stone which fills one of the 25 points on the board. Then after every white move, black must move to maintain the dominance. So even though black gains a point by ultimately capturing the white stone played, they also had to fill in a point to ensure that capture and black is held steady at 24 points.
In Chinese scoring, that first move doesn’t reduce Black’s score, so they ultimately end up with 25 points.
Or to put it in a more mathy context… In Chinese scoring, the total points scored (by both players combined) will always be exactly equal to the number of intersections on the board. In Japanese scoring, the total score will aways equal the number of intersections minus the total number of stones on the board. In order to have first move advantage, Black must play at least one stone which inherently reduces the combined score for Japanese rules by one point, but doesn’t affect the score at all using Chinese rules.
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