the objective of this paper is to study the spatial distribution of the Aridity Index in China during the period 1991-2000. Besides, the arid and humid is classified based on the Thornthwaite method, with the help of the climatic data including the monthly precipitation and temperature from 193 meteorological stations. The results showed that the temperature and precipitation was decreasing from the southeast to northwest. The potential evapotranspiration was higher in west than in the south. The aridity index was higher in southeast than in the northwest. The Penman method boundary was from the Liaoning Province to the southern Qinghai-Tibet Platean. The Thornthwaite boundary is low latitudes, which is from Shandong Province to Sichuan Province.