Abstract: In order to reveal the impact of forest vegetation changes on flood events in mountainous areas of Beijing, the control sections of the Yongding River and Daqing River basins were selected to analyze the vegetation cover changes and flood events before and after afforestation activities, and compared with the flood events of the "23·7" basin extremely heavy rainstorm in Beijing. The results showed that the proportion of cultivated land and forest land in the land use types of the Yongding River and Daqing River basins was relatively large, especially in mountainous areas, where forest land coverage was the main area. Since the large-scale afforestation activities in Beijing in the 1980s, in 2020, compared with 1980, the coverage of forest land and sparse forest land in the Yongding River Basin increased by 6% and 12% respectively, and the coverage of forest land in the Daqing River Basin increased by 73%; The change in vegetation cover can have a peak shaving effect on smaller floods, significantly reducing their runoff coefficient, but its effect on larger floods is not significant.