Plants experience dynamic light environments in the field, and the mechanisms for physiological and biochemical acclimation to fluctuating light (FL) vary among species. How soybean (Glycine max (L.) Merr.) integrates multiple physiological changes to acclimate to FL remains unclear. This study evaluated the impact of FL conditions on soybean morphology and photosynthetic characteristics by analyzing changes in photosynthetic gas exchange parameters and chlorophyll (Chl) a fluorescence parameters under alternating high and low light conditions. Results showed that soybeans subjected to FL conditions had low dry matter mass, small and thin leaves, and a low Chl a to Chl b ratio, resembling the traits of soybeans grown in low-light environments. However, their photosynthetic gas exchange rates and photosynthetic capacity remained constant, which was not the case under consistent low-light conditions. The adaptation processes for fluctuating and lowlight conditions are distinct. Correlation analyses indicated that the drop in carbon assimilation under FL primarily resulted from two aspects: the speed of recovery in stomatal conductance when transitioning to bright light and the slow relief of nonphotochemical quenching as light levels decreased. Thus, the decrease in carbon assimilation under FL conditions cannot be ascribed to adjustments during low-light phases but is due to a lag in photosynthetic response.