By using a one-dimensional raindrop category model and taking the aircraft observations of raindrop size distribution in the air and meteorological elements' profiles in the boundary layer as the initial background field,the evolution of raindrop size distribution during the falling process was simulated and analyzed.The results showed that the one-dimensional raindrop category model could simulate the evaporation,coalescence and breakup processes of the raindrop properly.The simulated raindrop spectra presented a multi-peak distribution.Evaporation would make the diameters of raindrops smaller.It affected small size raindrops more seriously than big size raindrops and increased the concentration of number of medium-sized raindrops,but it would not to change the overall spectral shape of raindrops.The multi-peak raindrop size distribution was caused by the coalescence and breakup mechanism,which were key factors in the change of raindrop spectra.