Abstract: The impact system and physical characteristics of the heavy rain process of Yunnan province which occurs in 6 August,2012 is analyzed.It shows that the major impact system of the province's strong precipitation process is the easterly air stream landing weakened tropical low-pressure system peripherals;It is energy-intensive areas over the Yunnan province and the atmospheric stratification is in unstable state before the heavy precipitation starts.Most of Yunnan in a high humidity area and the humidity conditions of northwest Yunnan is better than other area before the heavy rain occurs in water vapor condition.When heavy rainfall occurs,easterly air stream transports a lot of water vapor to most areas outside the northwest of Yunnan.The easterly air stream is the favorable water vapor conditions to provide precipitation maintaining.There is moisture convergence in central Yunnan and the eastern of Yunnan before the process starts and during the major precipitation periods.But the moisture convergence maintains a short time.During the heavy precipitation occurs,the vertical movement provides the favorable dynamic mechanism meanwhile the upward motion releaseas the unstable energy.