For shorting the tracing path of robot fish heading ball, and improving the efficiency of finding out target point, the writer introduces the tracing strategy of robot fish based on string endpoint algorithm. Based on improvement of tangent circle algorithm, give the design for string endpoint algorithm. Offer a series continuous target points for robot fish, by approaching the best contact point as close as possible by drawing the perpendicular bisector of an auxiliary circle’s string. Compare tracing situations of 2 algorithms, the results show that the strategy promotes a shorter tracing path, which result in a smoother track when fish head the ball into the goal.