Effect of water stress on Citrus photosynthesis characteristic was studied by using Yamasitaka, Newhall orange, Shatian pomelo as materials. The results showed: chlorophyll content of Citrus is significantly decreased by water stress, there are positive relationship between relative water content of soil and the volume of chlorophyll-a/chlorophyll-b. There are positive relationship between relative water content of soil and net photosynthetic rate (Pn) and transpiration rate, when there is a negative relationship with stoma resistance. Under well water condition, the diurnal variation of net photosynthetic rate of Shatian pomelo, Yamasitaka, and Newhall orange present bimodal curve, but the value and appeared time of peak are different among three varieties. Under water stress, the diurnal variation of Pn of Shatian pomelo show one peak while Yamasitaka, Newhall orange present two peaks. The diurnal variation of Pn of Yamasitaka present bimodal curve, under well water, 60%PC and 40%PC treatments. However under 20%PC treatment, Yamasitaka show single curve.