Abstract: The artificial island outside of a sea is composed of steel cofferdam and sand filling in the island. The steel cofferdam inserts the impermeable soil layer. The soft clay ground of artificial island is treated by surcharge preloading with PVDs. In order to know the settlement of soft clay ground with steel cofferdam, the numerical analysis is adopted. The results of numerical analysis are compared with the field monitoring data. Through back analysis of the calculated and monitoring data curves, the parameters are modified, and more reliable results are achieved. From the results, the steel cofferdam restrains the lateral deformation of soft clay ground. The failure plane of soft clay ground is hard to form. The settlement velocity is farther greater than that defined in the relative code. So the settlement velocity rule of the relative code should be broken for such special structure. At the same time, the residual settlement is calculated by means of the numerical analysis method, and its value is 9 cm. The consolidation settlement is completed two years later after the project completion. The calculated results may provide reference for the period of its use.