By using the GRAPES artificial precipitation model, a precipitation process on July 4, 2008 in Chongqing is simulated. and the characteristics of vapor distribution, cloud microstructure, microphysical conversion and artificial potential are analyzed, the results show that: in this precipitation process, the water vapor is extremely rich in Chongqing, and the vapor distribution is corresponding to the topographic distribution. Meanwhile, the lowlevel water vapor transport is large, the whole layer of water vapor flux is relatively high; with a moisture convergence, the cloud liquid water has a great impact on ground rainfall. Southwest air flow and terrain together provide favorable conditions for the formation of liquid water in Chongqing. There is a large amount of water vapor accumulated in the windward slope of northeastern mountain area, and easy to form a wealth of liquid water. In this precipitation process， a plenty of water vapor converted into cloud water in northeast of Chongqing， then it is rich in supercool liquid water， less in ice number， low in precipitation efficiency， and the vapor vertical flux is large at 0℃ layer， therefore it has greater potential for precipitation enhancement.