here are two similar southwest low vortices moving eastward on June 28-29,1996 and July 3-4,1996,but causing large difference in coverage and intensity of precipitation in Shandong. Study on it shows: the basic reasons that southwest low vortices cause different weather in Shandong are the differences of steering flow,physical mechanism and thermal structure,esp. the difference of steering flow. The movement direction of the southwest low vortices is decided by the steering flow,but the development is decided by the intensity of aerological thermal advection. The weather pattern of rain gust in Shandong caused by southwest low vortices is given. The results give us some references in the operational forecast.