During the driving process of the fuel tank of a passenger car, the vibration caused by the road bumps causes the oil to shake in the fuel tank, and the oil shake is mainly in the periodic up-and-down form, which is easy to produce cracks on the fuel tank. In order to explore the influence of oil on the fuel tank under periodic load, the modal and harmonic response analysis of the fuel tank is carried out using finite element analysis software based on the vibration durability test. The inherent characteristics of the fuel tank are obtained through this analysis method, and the displacement frequency response and stress frequency response results are verified and calculated through harmonic response analysis. The risk area of the fuel tank structure under the actual load is found through displacement frequency response and stress frequency response to determine whether it meets the vibration durability requirements. This analysis method can quickly find the weak points of the fuel tank structure under periodic load, predict and prevent the safety problems caused by external load vibration of the fuel tank; it will provide theoretical basis for the forward design of the fuel tank, shorten the design cycle and reduce the production cost.