Abstract: The purpose of this' paper is to study the diffusion of point source in the convective clouds.Considering the rising speed in clouds changes with altitudes we obtained the solution for the diffusion equation.By taking advantage of the mean figures concerning convective clouds in South China and the usual altitudes of point source at which the shell charged with AgI is exploded,we have calculated the distrition,with time of the diffusion range and concentration of the catalytic agent.