This paper introduces a controlling system of high speed stepping motor which combines singlechip and serial communication. This system contains the upper machine which is a PC, and the lower machine which is a singlechip. The upper machine communicates with the lower machine through serial port. An accelerating process is required because corresponding pulse frequency of regulated rotating speed is much greater than startup frequency of stepping motor. Accelerating program is written by compiling language and transition time can be precise to microsecond, which assures stability of accelerating process. This paper compares transition time and stability between exponential accelerating curve and uniform accelerating curve. Transition time is shorter and accelerating process is more stable for exponential accelerating curve.