Abstract: In order to explore the evapotranspiration of evergreen trees in Beijing Mountainou Area, the dynamic change of Pinus tabuliformis transpiration in the West Mountain Area of Beijing was continuously and high-precision measured in June 2010 using large-scale weighing lysimeter. Combined with the observational data of meteorological factors, the correlation between transpiration intensity and meteorological factors was analyzed. The results showed that: In sunny days, diurnal variation of transpiration of Pinus tabulaeformis showed a single-peak curve trend and the maximum was found at noon, which was in accordance with the solar radiation intensity and the temperature. But in rainy days,it showed the multi-peak curve trend. Transpiration intensity (Ti) was significantly related to atmospheric temperature (Ta ), relativeair humidity (RH ), canopy net radiation (Rn ) and vapor pressure deficit (VPD), the regression equation was Ti =2.228 -0.07Ta -0.032RH -0.002Rn +1.108VPD.