Abstract: To elucidate the daily change rule of photosynthetic characteristics heterosis of hybrid wheat and their correlations with environmental factors, common wheat hybrid‘Shaanken No.6’and its parents were taken as materials in this study and the photosynthetic parameters were measured respectively at the flowering stage, early grain filling stage, middle grain filling stage and post grain filling stage by using Li- 6400 photosynthetic system, and then the heterosis of each parameter was calculated and analyzed. The study showed that heterosis of net photosynthetic rate and stomatal conductance were the weakest at flowering stage, but they were the strongest at middle grain filling stage. At the early grain filling stage, the net photosynthetic rate was positive heterosis in the morning and negative heterosis in the afternoon. The stomatal conductance was negative heterosis in the morning and positive heterosis in the afternoon. Heterosis of transpiration rate was the weakest in the early grain filling stage and the strongest in the middle grain filling stage. Heterosis of water use efficiency was the weakest in flowering stage and the strongest at the early grain filling stage, and then it started to decline from the post grain filling stage. Grey correlation analysis indicated that air CO2 concentration was the key environment factor that influenced the photosynthetic heterosis of wheat. So high photosynthetic efficiency breeding should be conducted in the middle grain filling stage in order to develop the photosynthetic heterosis of wheat efficiently. Meanwhile, water use efficiency should be handled rationally at different development stages in field management.