Abstract: The effect of helicopter fuselage on its rotor is studied using a simplified free-wake model. The results show that the rotor near-wake is distorted because of the flow field of the fuselage, resulting in large variation on the induced velocity distribution at the rotor plane. The variation of the induced velocity distribution at the rotor plane caused by the fuselage through distorting the rotor near-wake is much larger than that induced by the fuselage directly.