Based on the momentum source method, a numerical calculation and analysis method for the rotor/propeller/fuselage interaction characteristics of a high-speed helicopter with double-thrust-propeller was developed. The momentum source was used to replace the rotor and the propeller. Firstly, numerical examples of isolated rotor and rotor/fuselage interaction were given to verify the accuracy of the numerical method. Then, the disturbing flow field in the hovering and forward flight state of the double-thrust-propeller high-speed composite helicopter was numerically simulated by using the constructed method. The disturbance of the fuselage to the hovering flow field and the rotor/propeller/fuselage interaction characteristics at different forward flight velocities were analyzed. The calculation results show that the blocking effect of the fuselage on the airflow reduces the lift of the rotor while the propeller is under the rotor. The acceleration of the wash air increases the lift of the rotor; the rotor/propeller/fuselage interaction is greater at low-speed forward flight, which is mainly reflected in the deflection of the propeller slipstream caused by the downwash of the rotor and the increase of the pressure distribution on the upper surface of the wing, while the interaction is smaller at high-speed forward flight.