Aiming at the realization of the sun-calibrated optical path switching component of the space-borne differential optical absorption spectrometer, a stepping motor control system based on BM3803 is proposed. The switching of the optical path can be realized by rotating the concave mirror with torsion spring driven by the stepping motor. Firstly, the open-loop control system of stepping motor based on domestic aerospace chip BM3803FMGRH and special drive chip LMD18200 is designed. Then the control circuit based on BM3803FMGRH and the drive circuit of LMD18200 are constructed, and the control program of stepper motor is programmed. When the stepping motor rotates 89 steps, the torsion spring rotates at an angle of 80.1°, the micro switch is turned on, and the optical path is switched successfully. It provides a reference for the design of the subsequent space-borne differential absorption spectrometer.