Seaplane landing is a strong nonlinear gas-liquid-solid multi-phase coupling problem. In this paper, Arbitrary Lagrangian-Eulerian (ALE) method is used to study the landing process of seaplane at different initial attitude angles and velocities. Firstly, a comparative study of the structure entry model and the air cushion model of flat impact water surface were conducted to verify the reliability, and the influence of the velocity, water shape and air cushion were accurately analyzed. Subsequently, the influences of vertical acceleration, attitude angle changes, aircraft impact force, and flow field distribution are analyzed. The results show that the air cushion has a great influence on the landing of seaplane. The cushioning effect of the air cushion becomes more pronounced with higher initial horizontal velocities. The disappearance of the air cushion will cause the tail part to impact the water surface twice and produce a pressure value beyond the initial value, which may cause damage to the seaplane. The initial attitude angle will affect the contact position between the seaplane and the water surface, with a greater angle resulting in a more significant air cushioning. This study provides a range of suitable speeds and attitude angles for the seaplane takeoff and landing process.