This study assumed the competitive structure based on genre classification for Korean online game market, and carried out the analysis on the degree and characteristics of the competition that appear differently in each sub market classified according to the genre. Analysis result can be summarized as follows. (1) In the view of the total play time, the proportions of the online games in each genre were appeared in the order of "RPG > FPS/RTS > Sports > Arcade/Poker > Go-stop > Board/Racing". (2) In the view of the shares in the play time, the degree of competition between games in the sub market structure of the online games according to the genre was found in the order of "RTS > Racing > FPS/Sports > Go-stop > Poker > Arcade/Board > RPG". The evaluation and interpretation of the high and low of the competition degree are as follows. As the degree of competition is higher, (RTS > Racing > ${cdots}$) the royalty and the ratio of reusing of the users for the game is lower, and on the other hand, the tendency of replacing and using appeared higher, so the market entry barrier for a new game can be evaluated to be low. Reversely, as the degree of competition is lower, (${cdots}$ > Arcade/Board > RPG) the royalty and the ratio of reusing of the users for the game is higher, and on the other hand, the tendency of replacing and using appeared lower, so the market entry barrier for a new game can be evaluated to be high.