Abstract: The relation between the total application of nitrogen(N)and the crop data such as the leaf area index (LAJ)，the dry matter accumulation and the components of the yield is analyzed according to the data got from the field experiments．Then the model of relation between the total N and the rice yield is established．The line of the relationship between the total N and the rice yield diversifies like a parabola，which means that with the total N increa sing ， the yield increases ，but after the total N increases to a certain value，the yield descents．That is，the return from the deal gradually decreases．The test of total N applied on the farmlands of higher fertility and lower one indicates that their optimum applications of N are quite different from each other．