In order to study the impact of liquid sloshing on the fuel tank during vehicle driving, The fluent finite element simulation software was used to simulate the truck fuel tank under braking condition in this paper, The fuel distribution and pressure distribution in each time period were obtained, and The results of fluid simulation were used as load input to get the stress of fuel tank under fluid structure coupling. The results show that liquid sloshing has a great influence on the stress of the fuel tank. The maximum stress of the fuel tank is 90.256 MPa in 0.5s, which is less than the yield strength. The structure of the fuel tank is reasonable. The results can provide data support for the structural optimization design of fuel tank.