The variety of the baseball's path is caused by the relationship between linear and spin velocity. It produced different aerodynamic behavior and the variety of path's offset. For the level of pitcher's performance the ball's linear and spin velocity are about 160km/hr and 35 rad/sec. In order to understand the path's variety, it is necessary to deeply study the ball's aerodynamic. This study utilized the numerical simulation method to probe the effect of baseball surface seam on drag coefficient. The result is showed that the higher the baseball surface seam's height the larger the drag coefficient. In addition, the baseball surface seam has the obviously effect to reduce the drag while the ball (radius is 7.4cm) velocity is up to 157km/hr.