Based on parameterization of cumulus and saturation moist static energy conservation principle in moist adiabatic process,by means of Clapeyron equation transformation,the cumulus parameters such as vapour of forming cumulus,the ratio of cumulus area and so on are calculated using partial realtime data and numerical weather forecast products.Furtherly,the convective precipitation is calculated by model.With empirical correction to the calculated value,the experimental forecast formula of convective precipitation is established,and the forecast result is quite good.