Abstract:To discuss the effects of different fertilizing concentrations on the diurnal variation of 12 physiological ecological factors of Carya illinoensis, such as net photosynthetic rate，stomata conductance，intercellular CO2 concentration，photosynthetic active radiation, thus providing rational fertilization basis for cultivating high-quality stock. The completely randomized trial was used to determine the diurnal variation of 12 physiological ecological factors of C. illinoensis seedlings, which were doused 0.3%, 0.6%, 0.9% and controlling the concentration of urea solution without fertilization. The correlation relationship between the factors was analyzed by correlation analysis, and the direct and indirect effects of physiological ecological factors on the net photosynthetic rate were analyzed by the main component analysis and the path analysis. It showed that the diurnal curve of net photosynthetic rate had a bimodal pattern and a clear midday depression. There was a close correlation between physiological ecological factors and net photosynthetic rate, the direct impact of the physiological ecological factors on net photosynthetic rate occurred in the order of relative humidity of air> stomata limitation> transpiration rate, the relative humidity of air was the primary determining factor, and the stomata limitation was the main limiting factor for net photosynthetic rate. The different fertilization concentration seedlings had higher photolytic efficiency than the non-fertilization seedlings, and the net photosynthetic rate of C. illinoensis seedlings with 0.6% concentration urea solution was the highest. Improving the relative humidity of air in the growth environment of C. illinoensis seedlings and limiting the transpiration rate of seedlings were important measure to improve the net photosynthetic rate.