This paper presents the exponential and the S-curve shape Acceleration/Deceleration(ACC/DEC) algorithm for step motor, aiming at solving the problems, such as out of step, impact and going beyond the limit. At first, the mathematical model and transfer function of step motor are built. In view of ACC and DEC process is symmetrical, so the paper only research and analysis the ACC control process of step motor.Then the paper presents the theory of the exponential ACC/DEC and the S-curve shap ACC/DEC methods and the design method. And implementing the design and simuliation of the system through the software Matlab. At last, it compares simulation results of exponential ACC/DEC control method and the S-curve shape ACC/DEC control method. The results show that the S-curve shape ACC/DEC control method smooths the speed transition and has more excellent dynamic and static performance and easy adjustment and improvement.