The maintenance of artificial beach in silt coast has been increasingly concerned. Based on the formula of sea bed erosion and siltation derived by the concept of equilibrium depth, through the assumption of equilibrium velocity, the sea bed scouring and silting caused by the change of water depth is added. The formula which is adapted to the calculation of erosion and siltation of natural seabed is generalized. The sediment scouring and silting of the beach dredging project in the new city of Lianyungang is calculated by the new formula. The result shows that the seabed tend to reduce to original depth after every dredging project is implemented. Mud is exposed and regular dredging maintenance is needed.