Abstract:By using routine observational data，satellites products，Doppler rada r products, the heaviest rainfall process of Shandong in 2008 is analyzed. The r ole of far distance typhoon in the increase of heavy rain when a westerly rai nfall system affects Shandong is discussed. The main precipitation period is sim ulated with MM5. The results suggest that wind direction and speed convergence z one of southeast air flow on the right side of typhoon Kalmaegi combines with we sterly convergence zone. Water vapor flux convergence makes vertical liquid wate r content increase significantly， and the specific humidity raised in the area southeast flow reached. A backward tilting trough in westerly causes positive vo rticity advection ahead of upper trough affecting the low impact system. Mesosca le meteorological modeling shows that the vertical convection is stable and the s trong symmetry instability makes ascending motion develop in the western region of Shandong in earlier stage. Increasing temperature and humidity in low level, symmetry instability and convective instability exist simultaneously and lead to the sustained torrential rain in Shandong Peninsula in later stage.