Abstract: The impact system and physical characteristics of the synoptic process of Dali in Yunnan province which occur in 27Aug,2010 is analyzed.It shows that the mainly impact system of the regional heavy rainfall is convergence zone between the Burma pressure and the West Pacific subtropical high in 500hPa and shear line in 700hPa.It is energy-intensive areas over Dali and the atmospheric stratification is in unstable state before the heavy precipitation starts.Low-level moisture is great and the convergence of water vapor is strong before the heavy rain occurs in water vapor condition.When heavy rainfall occurs,there is intense upward motion which releases unstable energy.The vorticity field which low-level vorticity is positive and high-level is negative and the divergence field which lower level is convergence and higher level is divergence is helping the upward motion development and heavy rainfall occurring.