Abstract: In order to study mechanisms of hailst one for mation and hail suppression with seeding and to obtain optim umseeding technique for hail cloud, a 3-D compressive numerical seeding model for hail cloud is developed. The water subst ance in hail cloud is divided into 8 categ ories, i. e., water vapor, cloud droplet, rain drop, ice crystal, snow, graupel, frozen drop and hail, and the detail micr ophysical processes are described in spectrum with two variable parameters and more reasonable paricle number/size distributions. Then, the model is able to predict concentration and water content of various particles. Especially, it can calcul ate number of hail stones which cores are graupel or frozen drop and apply to study mechanisms of hailst one form ation. Additionally, a conservative equation of AgI as seeding or glacigenicagent is found and nucleation by condensation of artificial nucleus, nucleation by freezing of cloud droplet or rain drop which contact with AgI particle are considered. The dynamic energy fluxo fhail shooting on ground is used to verify seeding effect. So that the model is used to study mechanisms of hail suppression with seeding and the seeding technique.