In order to study the ditching of aircraft and the influence of rear fuselage suction force on pitch attitude , the ditching of aircraft is numerically studied in detailed by using dynamic mesh method, user-defined function, six degrees of freedom model, volume of fluid model based on FLUENT software. On the beginning, the slamming coefficient, pressure distribution and free water surface of water entry of 2D circular cylinder are studied; Then, the vertical water entry of 3D elliptic paraboloid and the planing of 3D flat plate are simulated to validate the reliability of 3D numerical simulation method by comparing with the test results; Finally, the ditching of NACA TN 2929 aircraft model is also simulated, the results of which show that the rear fuselage suction force plays an important role in the change of pitch attitude and this method can be properly used to simulate the rear fuselage suction force and pitch attitude in ditching.