The high-fill foundation has large settlement, slow stability, and is prone to uneven settlement. Moreover, the complex nature of the fill soil and its creep characteristics have a significant impact on the foundation settlement. The oil tank foundation is highly sensitive to deformation. In order to evaluate the long-term deformation performance of the oil tank foundation at Guli high fill site in Southwest China, one-dimensional consolidation creep tests were conducted considering wet dry cycle, dry density, and load. Numerical simulation studies were then conducted based on the test results. The results show that as the load increases, the creep effect of soil is significantly enhanced, and the time required for creep to stabilize increases. With increasing dry density, the creep final cumulative deformation remains basically unchanged before rapidly decreasing. After experiencing dry-wet cycles, the soil develops cracks, and the binding force between particles weakens, meanwhile, the cumulative deformation increases. The effects of dry-wet cycles on the creep deformation of soil under various levels of load are different. Only when the load is less than the critical load, the effect of dry-wet cycles will increase the creep deformation of soil. Based on the creep parameters obtained from tests, a finite element analysis was conducted on the long-term deformation of the high-fill foundation for large oil tanks. It is found that under the condition of filling the oil tank with water, the settlement deformation of the foundation tends to stabilize after 1 year. After 30 years of operation, the settlement values of 1#, 2#, and 3# oil tanks increase by 0.47 ~ 2.03 mm, 0.71 ~ 1.52 mm, and 1.12 ~ 1.76 mm, respectively, compared to the calculation results without considering creep deformation. After considering the creep deformation of the fill soil, the calculated deformation index of the oil tank foundation still meets the control requirements of The Design Code for Foundation of Steel Storage Tanks (GB 50473—2008). The research results have reference value for the deformation design and calculation, and construction of similar high fill foundation for large oil tanks.