Abstract: The photosynthesis rate of leaves in field and their corresponding meteorological elements are observed in each growing season of winter wheat in North China. The light response curves are fitted for each development duration, and characteristic parameters are obtained such as initial quantum efficiency, maximum photosynthesis rate and convexity. In the entire growth season of winter wheat in North China, the initial quantum efficiency varies between 0.05 and 0.075, the maximum photosynthesis rate varies between 5 and 25 μmol·m^-2·s^-1. It is shown that the initial quantum efficiency of each development duration does not vary much and the maximum photosynthesis rate ranges from 20 to 25 μmol·m^-2·s^-1 before heading duration, and decreases greatly in reproductive growth duration, with the decreasing of nitrogen, phosphorus and potassium of leaves.