Abstract: In the report, the autumn rainstorm process in Haikou City（Hainan Province） in 2017 was selected as the research object, the raindrop size distribution data obtained by Parsivel precipitation particle spectrometer were used to analyze the microphysical parameters of the raindrop and the evolution characteristics of the droplet size distribution among the precipitation process. The results showed that the precipitation is mainly based on small raindrops with a diameter of less than 1 mm; the concentration of raindrops with diameter larger than 1 mm is relatively small, however, which has the greatest contribution to rain intensity; the raindrop concentration, rain intensity, maximum diameter and mean cubic root diameter have similar evolution trends with time, and the peak and valley positions are also similar. During the early stage of precipitation, the raindrop size distribution is dominated by single peaks and the spectrum is narrow; during the middle stage of precipitation, the spectrum is broadened, and the droplet size distribution evolves from single peak to double peak or even three peaks, there are 4 mm large particles appearing; during the terminal stage of precipitation, the spectrum is narrowed, and the droplet size distribution is changed back to single and the number of raindrops decreased significantly. The fitting of the Gamma distribution showed that the Gamma distribution fits the raindrop spectrum within the diameter range of 1.5 mm-3 mm, and the correlation analysis between the three parameters of the Gamma distribution and the precipitation intensity, which provides a reference for the further study on the microphysical characteristics of tropical precipitation clouds.