Abstract: The paper analyses on two Southwest vortex precipitation process during summer,2009.According to the analysis contribution iterms of the vorticity and thermodynamic diagnositic variable,we think that the main contribution of southwest vortex evolution comes from atmospheric convergence,secondly from vertical transport,the contribution from β-effect iterm is minimum and can be ignored.According to analysis several thermodynamic diagnositic variable,the results show that the release of convective available potential energy(CAPE) is earlier than the occurrence time of maximum rainfall.The onset time of extreme value of K index and Total index is slightly earlier than the occurrence time of maximum rainfall.The convective available potential energy,K index and Total index have a kind of indication meaning for precipitation forecast.