As the main tree species of farmland shelterbelts in North China，the transpiration rates of Pinus sylvestris L.var. mongolica Litv.

Larix gmelinii，Populus sdmondd XP. ndgra

and Populus alba XP. berolinensis were studied comparatively by the method of rapid weighting. Results showed that(1) the diurnal variation of transpiration rate of Pinus sylvestris L.var. mongolicaLitv. mixed with Populussimonii XP. ndgra and Pdnus sylvestrds L.var. mongoldca Litv. was of little difference，monthly variation of transpiration rate for them was the slowest，and the transpiration rates of other structures showed a parabolic trend.(2) Monthly averaged transpiration rate of Lardx gmelinii mixed with Populus sdmondd XP. ndgra accounted for 76. 96%of Larix gmelinii and the averaged transpiration rate of Populus simonii XP. nigra mixed with Larrix gmeldndd was 17.43%lower than that of Populussimonii XP. nigra. The structure mixed with Populus simonii XP. nigra and Populus simonii XP. nigra could decrease the transpiration rate of the two tree species. (3) The transpiration rate of farmland protection forest was seriously affected by atmospheric temperature and solar radiation in a variety of environmental factors in combination. The transpiration rate showed the positive correlation with atmospheric temperature，solar radiation，and soil water content，but negative correlation with relative humidity and wind speed.