A two-way fluid-structure interaction analysis model for the dynamic response of the propellant tank was established to address the strength failure of the thin-walled structure caused by liquid sloshing in the rocket engine propellant tank under different mechanical environments. The volume-of-fluid method was used to simulate the sloshing fluid in the partially liquid-filled tank, combined with the vibration control equations of the structure and the two-way transfer of fluid pressure and structural displacement at the fluid-structure coupling interface, to achieve the two-way coupling solution for the response of the liquid sloshing and the tank structure. The coupled fluid-solid response of a propellant tank thin-walled structure under impact load was investigated using the established model. The stress time histories and spatial distributions of the stresses of the propellant tank were obtained, and the effects of key factors, such as material, filling ratio and shell thickness, on the dynamic response of the structure were numerically characterised. The results show that: the dynamic response of the propellant tank and the sloshing behaviour of the fluid inside the tank can be obtained at the same time by using the established model. The maximum equivalent stress of the tank structure increases nonlinearly with the increase of the filling ratio. The weak position of the propellant tank is located at the connection between the lugs and the shell.