In order to accurately and efficiently estimate the radar scattering characteristics of coaxial rotor highspeed helicopters, the radar cross section (RCS) characteristics of coaxial rotor highspeed helicopters and the influence of coated radar absorbing materials (RAM) on them are studied according to the application of RAM in stealth design. Firstly, the highfrequency method for calculating RCS is established based on the physical optical (PO) method for calculating the coating surface scattering of the target and the method of equivalent current (MEC) for calculating the coating edge diffraction. The effectiveness of the highfrequency method is proved by the calculation of the metal ball and the rectangular paddle of the helicopter coated with RAM. The radar scattering characteristics and the strong scattering source distribution of the two polar azimuths and the fuselage in the nasal cones, lateral and tail trapping are studied, and the method of locally coating RAM is used to stealth design. The study shows that the coaxial rotor hub and its fairing parts, the larger curvature of the nose and tail and the smaller curvature of the side fence are important strong scattering parts of the body. Strong scattering parts coated with RAM can effectively reduce the highspeed helicopter RCS in all the direction, and significantly improve its stealth performance.