On the basis of data obtained from the autumn field experiment in Henan County of Qinghai Province and the 3D cloud model of CAMS, the natural cloud development processes were studied. The results show that the precipitation in the experiment areas was mainly determined by cold cloud raining processes and resulted from the melting of graupels into the warm layer; rain water evaporation is the main mechanism of rain water decrease; graupels play an important role in precipitation and their formation is closely related to ice crystals. Ice crystals are the main sources of graupels, which are produced mainly by auto conversion from ice crystal to graupel and a few grow by collection of ice crystals. AgI seeding should be done before ice nucleus largely activated, so rain enhancement can be improved by increasing ice crystals and decreasing super cool water.