Abstract: Photosynthetic characters and water use efficiency of Pinus densiflora grown under three soil moisture conditions were examined for two-year-old pot-cultured seedlings. The results show that net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Sc) and water use efficiency (WUE) of the seedlings and their diurnal variations of Pinus densiflora are all significantly different between light stress (LS) and moderate stress (MS) of soil moisture. Under the moderate stress of soil moisture, mid-day depression in net photosynthesis starts ahead by one hour and its duration is longer, both Pn and Sc are decreased, and the decrease in daily mean of WUE is less than that of Pn.