Abstract: With certain channels of the non-hydrostatic MBG(Meso-Beta-Gamma) model of CAMS/PRC, the May 3. 1990 precipitation processes over Asir mountain was two-dimensionally simulated. The results showed complicated features and mechanisms of the convection development, involving the dynamic and microphysical interactions between the clouds and orographic forcing. The distribution, evolution, sizes, top heights, updrafts and precipitation growth etc. of the modelling cumulonimbus clouds were generally consistent with field observation of the SACPEX projects. In addition, certain sensitive experiments on microphysics were also taken.