The contact pressure between soil and the flexible foundation under top uniform load is uniformly distributed. The additional stress of subsoil is large inside and small outside, which causes that the settlement of flexible foundation is also large inside and small outside. But the contact pressure between soil and the rigid foundation under uniform load is large outside and small inside, and the settlement is uniform. The thickness of the raft foundation of oil storage tanks is always large but not as large as that of the rigid foundation. So the distribution of the contact pressure is between that of the flexible foundation and the rigid foundation, and the settlement of the raft foundation is large inside and small outside. The authors adopt the UH model(the unified hardening model) as the soil constitutive model to simulate the soil deformation and research the sensitivity analysis of main influencing factors for the nonuniform settlement of the oil tank foundation. And the authors also research the influence of variable stiffness as on the nonuniform settlement.