In this paper, isentropic potential vorticity (IPV) theory is used to investigate a precipitation process in summer, which occured in Xinjiang of the Northern Qinghai-Xizang Plateau. The structure of atmospheric dynamic process associatted with precipitation is discussed. The results show that with the development of synoptic system, gradient of sloping to the north of isentropic surface in this region increassed, updraft enhanced here, so precipitation was influenced. The positive advection of IPV in IPV peak area make sense to forecast region in which it would be rain. The influencing system at surface mainly caused by frictional effects in planetary boundary layer frequently are high pressure ridges.