In order to find the most appropriate direction gear control for all the swimming robot-fishes’ speeds, the writer introduces an underwater robot fish direction gear control system based on PID algorithm theory. Analyze PID control principle and use it in underwater robot fish direction gear control, design PD algorithm for robot fish heading model, and give the application method and debug thoughts. The test results show that the algorithm can compensate the disadvantages of racer uses the tradition algorithm, the robot fish can debug direction and gesture rapidly and stably. The robot fish can freely swim in the water with the ball on its nose.