Abstract: In order to understand effects of frequent wind-sand flow on photosynthesis and water metabolism of Pinus sylvestnis var. mongolica seedlings, a field wind-sand flow experiment with a gradient wind speed treatments of 0 (CK), 6, 9, 12, 15 and 18 m/s (wind sand flow intensity are 1.00, 28.30, 63.28, 111.82 and 172.93 g/cm·min, respectively) was conducted in the Horqin Sand Land of Inner Mongolia in the Spring, 2013. The photosynthetic rate (P_n), transpiration rate (T_r) and water use efficiency (WUE) were investigated. The results showed that, 1) frequent wind sand flow could change diurnal variation pattern of the T_r, stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and WUE in the Pinus sylvestnis var. mongolica seedlings, but had litter effects on diurnal variation pattern of the P_n; 2) With increase of wind-sand flow strength, the RWC and leaf temperature, average daily P_n, WUE tended to decrease, which decreased by 4.6%, 1.8%, 52.6% and 56.3% in the 18 m/s treatment than that in the CK, respectively; and the average daily T_r, G_s and C_i tended to increase, which increased by 31.6%, 75.0% and 30.9% in the 18 m/s treatment than that in the CK, respectively. 3) With increase of wind-sand flow strength, the daily maximum P_n and WUE tended to decrease, the maximum daily C_i tended to increase, the maximum daily T_r decreased when wind-sand flow was below 15 m/s and increased when wind-sand flow was in 15 m/s and 18 m/s. 4) In wind-sand flow stress, decline of photosynthetic ability in P. sylvestnis var. mongolica scapling mainly due to decrease of the relative water content (RWC) and leaf temperature and the leaf mechanical damage, and increase of the T_r was attributed mainly to significant increase of the G_s.