By using the method of heat pulse stem flow technique, a long and continuous observation on the Qinghai spruce stem sap flow was made in 2008. Qinghai spruce is the major local tree species, located in the high and cold loess of Datong Country's Qinghai spruce pure land, Qinghai Province. At the same time, the meteorological factors of radiation, temperature, relative humidity, rainfall amount, and wind speed are recorded by the automatic meteorological stations. Results show that the stem flow rate is of great difference because of their different trunk diameters. The change of the sample tree's stem flow rate of 20 cm trunk diameter is obviously greater than that of 10 cm trunk diameter.T he stem flow rate of 20 cm trunk diameter is of little difference month by month,but the stem flow rate of 10 cm trunk diameter is very different. Thechanges in M ay and August are greater, but in June, the changes are less.It's illustrated that when the trunk diameter has a smaller size,it is effected very severely by environment. But when the trunk diameter is greater,it has a strong ability of autoregulation and environmental adaptation. The rainfall amount is 409. 1 mm in the four months,on the verge of the whole year rainfall. Total transpiration quantity is 386.45 mm.It lakes of water about 38.71 mm in May. The amounts of surplus rainfall are 74. 68,20.92 and 45.76 mm in June，July,and August,respectively.