Using the precipitation data observed by a laser optical Precipitation Particle Spectrometer, from March to June,2009, Gamma Rain Drop Size Distribution（Gamma DSD）function is assumed and the parameters of the function are determined by moment method. Characteristics of Gamma DSD and its parameters of precipitation of different types are analyzed. Moreover, the relationship between the parameters of “Normalized” Gamma DSD and rainfall rate is discussed, as well as the parameters and radar reflectivity factor. The result shows that the precision of different types of precipitation fitted by Gamma DSD in this experiment is available. As compared to the parameters of Gamma DSD, the parameters of “Normalized” Gamma DSD is more significant. When the radar reflectivity factor(Z) increases, the parameter μ gradually decreases, but the other parameter Dm increases exponentialy.