On the basis of the sound data obtained from the autumn field experiment in 2002 in Henan country of Qinghai province,and in terms of the 3D cloud-model of CAMS,the paper studies the natural cloud development and simulates the effect of seeding time,seeding position and seeding amount on precipitation enhancement.The study shows that the precipitation in the experiment area is dominated by cold cloud precipitation processes and the ice crystal is the main source of grauple,which is produced by the auto-conversion from ice crystal to grauple and then grows through collecting ice crystals.AgI-seeding should be done before the activation of most ice nuclei start,so as to enhance rainfall through increasing ice crystals content,and deleting super-cooled cloud water.Otherwise,there will be large amount ice crystals grew in natural clouds,artificial nuclei would be useless.