Three factors affecting the siltation thickness in an approach channel are briefly described and the computation methods for the siltation thickness in the channel of mud coast are reviewed. The results show that the difference of the concentrations under the action of breaking waves and normal waves is very big. But the computation method of the siltation thickness in approach channels derived from the mud coast can be used in the silty mud coast by considering the different hydrodynamic characters of breaking waves and normal waves and the movement properties of mud sediment and silty mud sediment. As an example, the sudden siltation thickness in an approach channel, located on the silty mud coast of Bohai Bay, China, is computed. The computation results agree with the actual siltation.