In this paper Doppler radar echo intensity values are converted into the relative humidity values, which are used to replace the relative humidity values of the same time in the MM5 initial fields. The result shows that by improving the model initial moisture conditions in the regional radar echoes, the energy was increased at the initial bottom , and the instability of convection was strengthened. Taking advantage of this, we can improve the precipitation forecast of the echo downstream region. The simulation experimentation is made to validate the method. The examples are a heavy rainfall event on July 16, 2004 and a hail event on June 14, 2005 in Linyi, Shandong.