Based on conventional observation data and NCEP 1°×1° reanalysis data, two typhoons, which entered Shandong by close sites but generated quite different rainstorm areas (to the northwest and northeast of the typhoon center, respectively), are analyzed to investigate the causes of asymmetric distribution of typhoon rainstorm. The results indicate that after entering middle latitude region, Typhoon HAIMA (2004) lies in front of upper deep trough and interacts with it, leading cold air intrudes into the typhoon circulation from the northwest side. Forced uplift of wet baroclinic frontal zone, confluence of cold and warm air, and water vapor convergence are generated and result in rainstorm event. The rainstorm tends to occur to the northwest side of the typhoon center, lying in front of high specific humidity and in the superimposed area of stronger water vapor convergence zone and the equivalent potential temperature front zone. By contrast, the interaction between Typhoon MATSA (2005) and the subtropical high brings about the asymmetric change of vorticity and vorticity advection, and the rainstorm area corresponds to the positive vorticity area or the positive vorticity advection at 500 hPa. The rainstorm tends to occur to the northeast side of the typhoon center, which is the superimposed area of strong positive vorticity advection area and water vapor convergence.