When the coaxial rigid rotor helicopter is flying at high speed, the hub has complicated flow, strong separation and large drag. In order to clarify its drag characteristics and flow mechanism, the CFD method is used to carry out numerical simulation research on the coaxial rotor hub model which has been tested in wind tunnel. The drag distribution, surface flow and spatial flow field characteristics of each component of the rotor hub are obtained. The components with the greatest drag and the main factors influencing the drag are explained. The drag reduction mechanism of the design parameters of the intermediate shaft fairing and pylon is revealed. The analysis results show that the hub of the upper and lower rotor blades is the main component of drag.The separation wake of the intermediate shaft and pylon has a great interference effect on the surface of the hub faring, which causes the flow separation on the surface of the hub fairing.The intermediate shaft fairing and pylon with moderate reverse pressure gradient can effectively reduce the interference of the separated wake flow to the hub faring and reduce the drag of the whole coaxial rotor hub system.