Abstract: A numerical model for simulating the photosynthesis of soybean canopy was established. The model includes sub-models for simulating diurnal variations of radiation. Temperature and CO2 density as well as the plant physiological sub-model which includes photosynthesis and respiration of soybean leaves. The results show that the mean error is about 8.7% when it is used for simulation the diurnal variation of photosynthesis in soybean canopy, and the model can simulate the process of midday depression of photosynthesis in soybean canopy accurately. Influence of the single factor on canopy photosynthesis was given by numerical analysis using the model, which provides a theoretical basis for raising the yield of soybean in Huanghuaihai Region.