The phase modulation mode is a critical parameter of the liquid crystal spatial light modulator, with significant influence on the interferometric image quality. In this study, we analyze the impact of mode-mismatch, caused by phase modulation errors in a single modulation cycle, on the interference fringe image quality, based on the modulation accuracy and device structure of the liquid crystal spatial light modulator. Our results demonstrate that improper phase modulation modes, in conjunction with limited modulation accuracy and device structure, can lead to phase shift distribution deviations in the interference fringe image that fail to meet the prescribed accuracy requirements, thus severely compromising image quality.