Ingredients-Based Methodology (IBM) was applied to forecasting heavy rain of Meiyu front. The basic ingredients of heavy rain is explained by the prime equations of precipitation, and the approach to construct ingredients is also indicated. Furthermore, by analyzing a case, the application of the IBM to the prediction of heavy rain is illustrated. The result indicates that some basic ingredients, such as precipitable water (PW) etc., selected by basic physical mechanism of severe convective weather, have good relationship with the heavy rain in Meiyu front, and the potential prediction of heavy rain can be made by the meteorological process of these basic ingredients.