Abstract: Grain size analysis was conducted on 57 surface sediment samples collected in the waters of the Hong Kong-Zhuhai-Macao Bridge in May 2021. The sources and controlling factors of each end-member composition were discussed by combining grain size end-member analysis and grain size trend analysis techniques. Results show that the average particle size of the surface sediments was 1.95～7.45Φ, mainly muddy silt and sandy silt types, and could be divided into three particle size end-members: muddy end-member (M1), fine silt end-member (M2), and coarse silt or fine sand end-member (M3). M2 and M3 were mainly distributed in the northwest of the bridge, and M1 showed a trend of migrating to the southwest. M3 was mainly distributed in the southeast of the bridge, showing a trend of migrating to the northwest. The distribution and migration trends of M1 and M2 are mostly consistent with those of suspended matter, being mainly affected by runoff sediment input. M3 is mainly distributed in low suspended-matter concentration area and was greatly affected by tidal dynamics. The surface sediments before and after the construction of the bridge showed an obvious coarsening trend, which may be mainly related to the reduction of runoff sediment input and the enhancement of tidal dynamics in the Lingding Yang (Bay) in recent years.