The arbitrary Lagrangian-Euler method and penalty coupling method are used to simulate the helicopter-floats landing on calm water， and the mechanical and flow field characteristics of helicopters and floats are analyzed. Results show that before water impact of the helicopter， the floats play a role of energy-absorbing and buffering by compressing the air in the floats which is deformed by water. Compared with helicopters without floats， the peak impact acceleration of helicopters can be reduced by 69%. At the initial stage of landing， the high-pressure areas of the water are near the bottom of the helicopter， the front end of the floats and the back-installation point. There are two high-pressure areas at the bottom of the helicopter， and the distribution of pressure along the width of the body has a clearly three-dimensional effect. Moreover， the large stress concentration occurs at the front/back installation points and an arc area between them. The maximum equivalent stress is 193.9 MPa， which appears near the front installation point of the float， and the floats are not damaged.