To analyze the characteristics of suspended sediment diffusion caused by excavation underwater,we take an excavation project of a channel on the south side of Culu island in the Minjiang estuary for example,to study the relationship between the diffusion of the suspended materials and the water depth and tide types by a two-dimensional numerical model.The results show that both the increments of suspended load concentration and the areas in which the increments of suspended load concentration more than 10 mgL are larger with shallow excavating sites or neap tides,because the suspended sediments are hard to diffuse.