Abstract: In order to further study the typhoon ‘Muifa’ effects in the process of rainstorm caused by typhoon mechanism, to have a better grasp of the rainstorm process. Based on the NCEP 1°×1° reanalysis data on 5th-8th August 2011, a study on the heavy storm in part of Shandong Province under the influence of the typhoon Muifa was conducted. The results showed that: the involvement of dry cold air had important influence on the weakening of the typhoon intensity. Dry air had some relevance with the heavy rain area, the rainstorm region lied in front of the dry air (the relative moisture was lower than 50%), where was the junction of the dry and wet air (the relative moisture was bigger than 50% between 600 hPa and 850 hPa). Meanwhile, the rainstorm region, which agreed well with the MPV1 and MPV2, was close to the negative areas of MPV1 and the positive areas of MPV2. Accordingly, there existed an isoline denseness area of MPV1 between 850 hPa and 925 hPa and MPV2 at 925 hPa.