A study is carried out on the data of suspended sediment particle diameter in the fixed vertical line tests in the South and North Passages of the Yangtze Estuary in 2018 and 2019.The distribution characteristics of the suspended sediment particle diameter in the South and North Passages in terms of time and space and their causes are analyzed, and the variation laws of the suspended sediment particle diameter and composition in the Yangtze Estuary under different hydrological conditions such as runoff and tide are explored.The results show that the particle diameter of suspended sediment in the Yangtze Estuary is between 0.007 0 and 0.016 8 mm, and is larger in the dry season than in the flood season, larger during spring tide than during neap tide, and slightly coarser during the ebb tide period than during the flood tide period.The water body in the upper layer has fine suspended sediment, the water body in the lower layer has coarse suspended sediment, and the water body in the middle is between the two.The particle diameter of suspended sediment in the North Passage is slightly coarser than that in the South Passage.The suspended sediment in the South and North Passages is fine sediment.The proportion of fine silt, very fine silt and clay with a median particle diameter of less than 0.016 mm is about 70%, the proportion of sediment with a median particle diameter of less than 0.005 mm is about 30%, and the proportion of sediment with a median particle diameter of more than 0.062 mm is about 7%.