With the mesoscale model MM5, the rainstorm process of Typhoon Wipha on 19 and 20 September is simulated successfully. Based on the MICAPS data and mesoscale numerical simulation products, the low pressure structure characteristics and heavy rain area of Typhoon Wipha are analyzed. It is found that there existed divergence at high altitudes and convergence at low altitudes. The heavy rainfall was produced by the convergence of abundant vapor in the southeastern Shandong and to the south of the Shandong peninsula, which was induced by the moist southerly stream from the sea at the right side of the typhoon. The wind speed of typhoon center was relatively smaller than that of the strong wind center on the sea, and the windspeed mates are formed between the two centers. The heavy rain mainly happened in the areas with large wind speed gradient between the windspeed mates in the midlow layer. Because of the landsea difference of the underlying surface, the physical structure of the typhoon under low pressure was eastwest asymmetric, and moreover, the upmovements over land and sea areas had different characters. The up movement of the sea areas was stronger and more unstable than that on the land. The heavy rainfall occurred in the eastern part of the inverted typhoon trough. The increment of precipitation was related to the remarkable pulsation downward movement of the highaltitude southeast jet, highaltitude positive vortex center, and negative divergence center.