The high speed coaxial helicopter with rigid blades will be the future of rotorcraft, which essential characteristic is the lift-offset of advancing blades. In order to research the influence of lift-offset on the rotor performance，the aerodynamic characteristics of advancing blade concept(ABC) rotor with different lift-offsets are calculated by the rotor free wake method. Through the analysis of the computing results，the effects of lift-offset on rotor lift distribution,lift-drag ratio,drag and power characteristics are obtained. The comparison and analysis of the results of advancing ratios μ=0.2,0.4,0.5 are also conducted. Results indicate that the rotor lift?offset plays a key role in the forward flight performance, thus changing the lift distribution on the rotor .The rotor lift-offset producing maximal lift-drag ratio varies with different advancing ratios. The maximal lift-drag ratio appeares at the lift-offset of about 20%,25%,30%when μ=0.2,0.4,0.5,respectively.