The initial fields of MM5 are improved in this paper by adopting an initialization scheme of simultaneously adjusting thermodynamic and dynamic variables and coordinating humidity and temperature changes,and by assimilating R-Zdata into the initial field.Experimental results show that the improved initialization of MM5 can raise the forecast accuracy of precipitation location and rainfall,expecially of 0～6h,and the thermodynamic variable adjustment is more important than the dynamic variable adjustment in improving the forecast of precipitation location.