Abstract: The major variation of greenhouse environmental factors and diurnal variation of photosynthesis of cucumber leaves and its relationship with yield were studied by designing different irrigation and nitrogen treatments in the greenhouse of North China. The results showed that the diurnal variation curves of PAR, Ta, RH and other environmental factors had a single-peak and the net photosynthetic rate and stoma conductance of cucumber leaves under different water and nitrogen conditions had two peaks. There was an obvious midday depression of photosynthesis and the stomata were the main limiting factors. The relationship between photosynthetic rate and yield of cucumber showed a quadratic curve. With moderately reduced water and nitrogen application rate, the net photosynthetic rate of cucumber did not decrease significantly, while the instantaneous leaf water use efficiency increased significantly. In our experiment, the highest yield was achieved with an irrigation quantity of 5190 m3/hm2 and nitrogen amount of 600 kg/hm2. Such practice can make the yield increase by 4.21 percent compared to the habitual water and nitrogen treatment. The general analysis showed that the optimization of water and nitrogen treatment resulted in a more rational management. This practice not only achieved a higher net photosynthetic rate and water use efficiency, but also a higher cucumber yield.