Abstract: To study the rainfall spatial distribution laws as well as the formation mechanism in China's Tianshan Mountains area, this thesis built the mountain area rainfall estimation model and analyzed the rainfall causes with the partial least squares(PLS) and GIS technology, based on the DEM in the research areas as well as the data information from the meteorological stations. The result shows that the rainfall in the Tianshan Mountain area is showing an obvious longitudinal and latitudinal zonality, with more rainfall in the west section than that in the east, and more in the north slope (windward slope) than that in the south slope (leeward slope). We can find a linear increase of the rainfall in the research areas with an altitude of 4 000 m below, and then a rapid decrease, with the second maximum belt at around 5 500 m. The rainfall and the slope are positively associated when the slope is less than 50°. When the topography lifts, the rainfall will increase with the drops of temperature and the rise of humidity, which is the requirement for the rainfall formation in the mountain areas. Generally, the method of PLS can effectively solve the multiple correlation issues between the rainfall and various factors, the regression effect of the model being obvious. This model has certain adaptability for the mountain area rainfall simulation.