Because there was little research on artificial island under the action of gravity, seepage, earthquake and other coupling forces, strength reduction dynamic analysis method was introduced to the dynamic stability on an artificial island. Establish finite element numerical model and use dynamic constitutive equations of Finn-Byrne as well as modified Hardin-Drnevich for this artificial island under earthquake. Analyze the scope of liquefaction, stress distribution, and dynamic stability. Calculation results show that: 1) this island can meet the requirement of dynamic stability. Because shear strength of muck layer is quite low, the final fracture surface is composed by the lower part of stone and mud layer under earthquake; 2) owing to precipitation, water seepage flow from outside to inside of the island, effective stress and liquefaction resistance of soil increase from the outside of the island, however, the ones from inside of the island get lower. So the soil from outside is more likely to be liquefied; 3) due to the constraints of surrounding soils, soil liquefaction won't lead to high deformation, only more liquefied soil can do. The results provide reference for dynamic analysis of the artificial island.