Abstract: Based on the prediction results of the "6. 26" sudden heavy rain in Mianning by SWC-WARR, the forecast effect of different model resolutions on the sudden heavy rain in mountainous areas was compared and analyzed, and it is concluded that: the fall area and the strength of sudden heavy rain in complex underlying surface area are sensitive to model resolution, the improvment of the model resolution can describe the complex terrain more accurately, make it closer to the real terrain conditions, and get more accurate local thermal and dynamic state, simulate small and medium scale weather system better, the improvment of the forecast results by increasing the model resolution shows that the characteristics of the rain belt are more clear, the strong precipitation centers are increased and refined, and the precipitation intensity is increased significantly.