Fuel sloshing within aircraft fuel tanks can generate significant forces and moments on the tank walls, thereby affecting the aircraft’s dynamic characteristics. To enable accurate and efficient prediction of sloshing-induced forces and moments, this study develops an equivalent pendulum mechanical model based on the finite element method. The study focuses on fuel within auxiliary and wing tanks at a 50% fill ratio. Using this model, the sloshing forces, moments, and the motion of the fuel’s center of mass are predicted under three typical flight conditions: pitch, roll, and yaw. The predicted results are further compared with those from computational fluid dynamics simulations, demonstrating the accuracy of the proposed model in capturing the dynamic response of fuel sloshing.