In order to examine the application capability of fourorder recursive filters on heavy rain forecast,by using GRAPES3D Var system，the paper numerically simulate the heavy rainfall in Sichuan Basin during July 16—19,2007.Three experiments were carried out in this study during different periods.The first experiment used oneorder recursive filter with one intrinsic scale;the second used fourorder recursive filters，which was synthesized from three fourorder recursive filters with different intrinsic scale respective;the last experiment used oneorder recursive filter，which was synthesized from three oneorder recursive filter with different intrinsic scale respective.The results show that the recursive filter with multiple intrinsic scales is better than the one with only one intrinsic scale.The heavy rain process is closer to the reality in the second experiment.The forecast of precipitation region and amplitude has been greatly improved.Its adjustment of vapor is more ideal.