Abstract: The results of rotors/fuselage aerodynamic interactions for the coaxial helicopter in hovering and forward flight were presented according wind-tunnel experiment. The presence of the rotor wake creates a significant down load on the fuselage which decreases with increasing advance ratio. The interactions above decreased in forward flight, but yaw moment was generated by fuselage; The interaction of coaxial rotors to fuselage changes when the tail plane area, and lower rotor pitch or advance ratio was changed. The interaction of fuselage to coaxial rotors is different from that of single rotor helicopter, such as: in hovering state, the coaxial helicopter fuselage has no obvious effect on rotors, the fuselage generates beneficial interaction to coaxial rotors when in forward flight and the interaction decreases as the advance ratio increases.