Abstract: By using the test method of pot planting, author has studied the influence of N application rate on photosyrithetic characteristic of lettuce. The study indicates that N application rate has influenced on not only yield of lettuce but also photosynthetic rate,light saturation point, light compensation point and chlorophyll content etc. When N application rate reaches up to about N3 level (N, 0. 15g/kg), the yield of lettuce turns out to be maximum. Any more N application rate beyond this level will otherwise lead to the decrease of yield of lettuce. Based on the outcome of the test, the relation between N application rate(X) and yield of lettuce (Y) can be obtained as follows:Y-8. 98+35. 101X-62. 779X2 Although content and photosynthetic rate etc. go up as N application rate increase,light saturation point reaches up to its maximum value 636 mol. m-2s-1 when N application rate is N3 level. That is, the utilization of strong light is more efficient. This is consistent with the change trend of yield.