The data of this paper includes two parts, one is the monthly average data of Outgoing Long-wave Radiation(OLR) from June 1974 to December 2005, which is observed by the National Oceanic and Atmospheric Administration(NOAA) satellites, there are altogether ninety-one grid points in the regions of 75°~105°E and 25°~40°N and the horizontal resolution ratio is 2.5°×2.5°Lon./Lat.. Another is the monthly rainfall data of ninety-three conventional meteorological station of the Qinghai-Xizang Plateau during the period of 1961-2005. On the basis of the relationship between rainfall and OLR and the partition of climatic zone, the mathematic model is established in each zone and grid, which is used for estimating the monthly rainfall, and then estimating the monthly precipitation latent heat year by year from 1961 to 2005. It shows that the annual average rainfall is 401.5 mm and the latent heat is 18.55×10²⁰J in the eastern part of the Qinghai-Xizang Plateau, which has some increase in recent 45 years, and the increasing rate is 0.218×10²⁰J/10a, that is to say, it will increase 1.2 percent in each decade.Furthermore, the total latent heat and its variability of the Qinghai-Xizang Plateau have a little greater than the eastern part.