The present paper analyzes the impact of mechanical shutter on the spectral image acquisition and processing of large-array filter-type multispectral imaging system. The final image quality relies highly on the mechanical shutter due to the fluctuation at exposure time. The conventional mechanical shutter’s structure and driving method was analyzed to find out the key fact for its poor stability. An improved method of mechanical transmission and circuit driving was proposed. Laboratory experiments showed that with the improved design strategy, the maximum rate of change between adjacent exposures was reduced from 15.05% to 0.96%, which is a great improvement of the exposure time stability. Field test was also carried out and the results show that the combined color images are closer to the realistic targets and no abrupt color change iwas found. It’s of great significance for practical application in multispectral image process, interpretation and target identification.