The researchers studied the grain size of sediments in the coastal waters of Shantou City. They found that the sediments are mainly clayey silt, sandy silt, and sand-silt-clay. The sediments contain gravel, sand, silt, and clay in different proportions. The sediments' mean grain size ranges from 0.12 to 7.30 mm. They classified the sedimentary environment into 4 types and analyzed sediment transport trends using a model. The sediments in Shantou harbor move towards estuaries and offshore, while in Zhelin Bay, they migrate from coasts/islands to the bay. These findings can help in making decisions for port and waterway engineering.