The frequency fiaing pulse width modulation and adjustable microstep-driven system is discussed. The system of the step-motor was controlled by the MCS-51 single-chip computer. The system is single-voltase driving. The system is confisurated the proprietary software. On the same hardware supporting,the numbers of the microstep can be changed by operating the keyboad. The system applies the technology of the digital frequency fixing PWM and the feedback control of the microcurrent. At the last, the articl brings up the new mothed which determins the state words of the equal-micro-step current by the experiments. The feasibility of this mothed is proved by the experiments.