Abstract: Application of General information,T639 numerical prediction products and physic live information,we diagnoses the circulation evolution and various physical characteristics in the process of drought to rain on August 14, 2011.Resuhs indicate that Hohhot over the long-term stability of the arid period ＂West to East high and low＂ circulation-type;adjustment of large scale circulation,particularly latitude circulation to ＂East West＂ change is a necessary condition of drought to rain.Further analysis found that the rainstorm contact with the Western Pacific typical subtropical high and West extending north,subtropical South-western perimeter of the warm, moist air enhancement,low level Jet, Vortex development of stratified shear and instability, and so on.Drought to rain precipitation mainly merge in the mixed area of energy of tongue in the lower,water vapor ＇senior and low-level convergence,and divergence in the updraft area.