Abstract: Using the conventional observation data，the automatic station precipitation data，0.1°×0.1°FY－2E cloud top brightness temperature data and 1°×1°NCEP reanalysis data，the main influencing system，water vapor source，dynamic and thermodynamic conditions for the strong precipitation process in east Sichuan on 20－23 July 2012 are analyzed，the results show that:(1) The 500hPa upper trough eastward to Sichuan and deepen development to south in the heavy rainfall process，cold air after trough and warm moist air before trough flows in Sichuan，the low－level has low vortex development，with the favorable situation of high and low－ level jet coupling; (2) The rainstorm early water vapor mainly comes from the bay of Bengal，as the typhoon in the South China Sea westward，the periphery of easterly flow westwards enhancement，the southwest warm moist flow northward is restrained，which make rain belt southward; (3) It is given priority to convective precipitation，the water vapor condensation latent heat plays a major role in the lower troposphere during the rainfall process，strong ascending motion carry low layer latent heating upward，form the heat source center in high layer，the heating of the atmosphere is closely related to the atmospheric vertical upward movement during the period of heavy precipitation．The main contribution is the vertical transportation item of apparent heat source Q1 and apparent moisture sink Q2 in this rainstorm，especially in the strong precipitation stage; (4) In the development stage of the low vortex，lower level positive vorticity local change first of all，in the waekening stage of the low vortex，the peak center of the total positive vorticity variation term uplift from the lower level to the middle and lower; (5) The mesoscale convective system consistent with the hours of precipitation distribution，MCS is one of the important factors that trigger precipitation．