Abstract: The parameter of the response of photosynthesis to CO2 is one of the most important variables in the crop growth models.The leaf photosynthesis of winter wheat varieties over decades was measured with Licor-6200 portable photosynthesis analyzer,based on which a simplified leaf photosynthesis model involved with CO2 direct impact was established.The key parameter μ,which was used to describe the response of leaf photosynthesis to the environmental CO2,was identified for each variety of winter wheat in different decades with the established model.Statistical analysis of the μ values indicated that it changed obviously between different varieties of winter wheat in North China Plain with a range from 0.57 to 1.02,but without any obvious time trend.The analysis result showed that correlation between μ,the initial quantum efficiency α and the maximum photosynthesis Pmax were lower,which provided the experimental prove for the valid of the simplified leaf photosynthesis model.This work surely could be referred in developing the winter wheat growth model in the North China Plain in the near future.

Key words: North China Plain, North China Plain, Winter wheat, Photosynthesis, Crop model