With the subsea production system applied more and more widely in China deepwater oil and gas fields, various kinds of extreme conditions are analyzed and applied in the subsea design. Subsea production system design in China is still in the initial stage. When seismic influence is analyzed and designed, equivalent loads are imposed merely for calculating the bearing capacity and safety, which cannot analyze the impact of seismic load to soil foundation. Aiming at this problem, the soil liquefaction and the settlement induced by strength degradation under seismically induced cyclic shear stress are analyzed. From the calculation result of a subsea project, it can be seen that analysis on soil liquefaction and strength degradation has important significance.