Abstract: To study the effect of water stress on photosynthetic characteristics of Pistacia weinmannifolia, according to the soil field capacity, the author set different soil moisture content gradients (W1-W6, with soil field capacity of 100%, 80%, 50%, 30%, 10% and 5%, respectively). With Pistacia weinmannifolia as material, the author used Li-6400 to measure the net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), stomatal conductance (Gs), transpiration rate (Tr) and water use efficiency (WUE) under 6 different soil moisture gradients, in order to understand the response of Pistacia weinmannifolia to too little or too much water stress, thus to provide certain theoretical guidance and technical reference for vegetation restoration, and breeding and cultivation of Pistacia weinmannifolia in dry-hot valley, Yunnan. The results showed that: (1) under different soil moisture gradients, Pn values of Pistacia weinmannifolia showed significant differences, total Pn presented a ‘down-up-down’ trend, diurnal variation curve was the ‘twin peaks’ type, with obvious phenomenon of lunch break; Pn decline was limited by stomatal and non-stomatal limitation factors, W1 and W2 were limited by stomata, W3 and W6 were limited by the non-stomatal factors; with the declining of soil moisture content, stomatal limitation tended to change to non-stomatal limitation; (2) after 18:00, except the W3, Pn of other treatments showed negative values, respiration was greater than the photosynthesis, the photosynthetic productivity of plants descended and finally the plants died; W3 was the best choice of the moderate moisture, its field capacity and soil moisture content were about 50% and 33.6%, respectively; (3) the stomatal conductance fell with the decrease of the soil moisture content, when the soil moisture content was in W3-W6, the daily change curve of stomatal conductance Gs had no obvious change, it almost had a gentle condition; the Gs value of W1-W6 was the largest at 8:00, mainly caused by air humidity; (4) the water use efficiency WUE increased with the soil moisture content, appropriate drought stress was advantageous to improve Pistacia weinmannifolia photosynthetic productivity and water use efficiency.