The transpiration rates of Pinus sylvestris L.var.mongolica Litv., L arix gmelinii , Populussimonii×P.nigra , and Populus alba× P.berolinensis , the main tree species of farmland shelterbelts in the semi-arid region in the wesTheilongjiang Province of China , were studied by using the method of rapid weighting.Results showed that the monthly variations of the transpiration rates were different and the transpiration rate of Pinus sylvestris L.var.mongolica Litv.was the slowest.The monthly variation of the transpiration rate of Pinus sylvestris L.var.mongolica Litv.was the least and the transpiration rates of other structures showed a parabolic trend.The transpiration rate of farmland protection forest was seriously affected by atmospheric temperature and solar radiation in a variety of environmental factors in combination , and the transpiration rate showed the positive correlations with atmospheric temperature , solar radiation , and soil water content , but the negative correlations with relative humidity and wind speed.