An efficient numerical simulation method based on the momentum-source method is developed for analyzing rotor-propellers interaction flowfield of the double-thrust-propeller configuration (X3 configuration) compound high-speed helicopter. In the method, rotor and propellers are represented by momentum sources, and the structured grid is applied to the interaction flowfield. Firstly, in order to verify the effectiveness of the method, isolated rotor, isolated propeller and rotor-fuselage interaction are taken as examples, and the calculated values are compared with the available experimental data. Then, by using the established method, rotor-propellers interaction flowfield of X3 helicopter on hover and forward flight is simulated, and the influences of different velocities and different flow angles are analyzed. Some meaningful conclusions are obtained.