A new method was developed to study how soybeans respond to salt stress by looking at photosynthesis and chlorophyll fluorescence. Two soybean varieties were exposed to different levels of salt stress for 15 days. The photosynthetic system of soybeans improved under low salt stress but got worse under high salt stress. Some important parameters like biomass and chlorophyll fluorescence decreased, but a specific parameter called qN actually increased under salt stress. This method could be useful for quickly and non-destructively detecting how soybeans react to salt stress in the field.