Abstract: Diurnal dynamics of photosynthesis characterics under 4 different soil water conditions were monitored using Potable CI-301PS photosyntheticsystem. The results summarized as follows: the curves of diurnal variation in transpiration rate and stomatal conductance in the four treatments had one peak, and all the peaks values happened at 12:00. The curve of diurnal variation in net photosynthetic rate of the four treatment were double peaks, and an obvious midday depressions at about15:00~16:00. The diurnal variation of water used efficiency were many peaks. Analysis of variance indicated that the Pn, Tr and Cond under humid condition and semiarid condition were significant higher than that under drought condition, and the WUS under saturated water condition were significant lower than other three treatments. Correlation analysis show that the Pn and Tr had significant correlation with light intensity and temperature, and significant negative correlation with relative humidity.