The B-model and the IAPAS (Institute of Atmospheric Physics, Academic Sinica) limited finemesh model are nested in one way,and three schemes, i. e., the tendency correction scheme, the relaxation method and the radiative lateral boundary condition scheme, are tested.Tests show that the stability for the integration using the first schemeis the best. Several heavy rain occurrences during the Meiyu period of 1986 are studied using the nested fine-mesh model, the forecasting results of which is greatly improved, with the accuracy of the rainfall values increased by more than 20% and the precipitation distribution closer to actual conditions. The nesting technique stabilizes the integration of the fine-mesh model, lessens the reliance on smoothing, and lengthens time validity of precipitation forecasting. The effect of the boundary conditions on the heavy rain system is also examined.