It is important and necessary to study the water landing overload of wing-in-ground(WIG) aircraft, as the damage or buckling step is most likely occurred in body steps, especially in double-stepped cases. The Arbitrary Lagrangian-Eulerian (ALE) finite element method was utilized to simulate the water landing of a wing-in-ground aircraft, and the penalty function method was used in the two-phase interface fluid-solid interaction problem. The effect of different parameters such as horizontal flight velocity, falling velocity, pitch angle on the immersion depth, and overload was analyzed. The results showed that the pressure maxima of the aircraft landing water all occur at the step in this paper. With the increase of the pitch angle, the peak of vertical overload rises and then falls, while the peak of horizontal overload keeps reducing. When the pitch angle is 7°, the vertical overload peak reaches the highest, which is 1.4 times that of the lowest overload in the pitch angle of 15°. On the other hand, the peak of the horizontal overload rises as the horizontal component of flight velocity increases, and it is visible that there is no discernible effect on the peak of vertical overload. Meanwhile, an approximately linear relationship appeared between the peak of vertical overload and the square of falling velocity in this paper.