Abstract: Based on ISCCP datasets (1983-2006), it is found that there is a high center of high cloud over the Tibetan Plateau and a high center of middle cloud over the Sichuan Province and the regions along the same latitude in East China; whereas a low center of middle cloud over the Tibetan Plateau. Present and LGM climates are simulated with a global climate model CCM3 nested with a regional model MM5. Comparison of MM5 modeled clouds and ISCCP data illustrates that the model can reproduce the main patterns of high and middle cloud over China, suggesting that climate characteristics of cloud might be determined by relative humidity as modeled clouds is simply a derivative of relative humidity. Meanwhile, the modeled results are in well agreement with NCEP data in the vertical distributions of water vapor and temperature. Based on the above verification results, the hydrological cycle changes during LGM are simulated and analyzed. Model results show that during LGM, temperature in the troposphere decreases with a high center of temperature reduction in the upper and middle troposphere in summer. There is a high center of temperature reduction in middle troposphere over South China in winter while temperature increases in upper and middle troposphere over North China. Water vapor changes are positively related to temperature changes. The water vapor generally drops with the maximum decrease near surface except that in upper and middle troposphere over North China in winter. The water vapor changes gradually weaken with height, but their relative changes reach the maximum in the upper troposphere. Relative humidity changes occur with the maximum of more than 15%. The relative humidity isn’t conservative on regional scale. Changes of middle and low cloud are consistent with the relative humidity changes. During LGM, high cloud reduces except in Southwest China, and middle and low cloud also decrease. Moreover, the low cloud reduction is the most in the three types of clouds. Precipitation changes correspond with the changes of middle and low cloud. Based on the changes of the relative humidity and effective precipitation, it is found that during LGM Southwest China became wetter, and Northwest China became wetter in summer.