For the drag of coaxial rigid rotor hub has a large proportion in helicopter, the study on methods of reducing drag is presented. Firstly, the basic type of hub fairing is determined by analyzing the characteristics of coaxial rigid rotor hub, and parameterized model of hub fairing is established. Secondly, the influence of parameters of fairing on drag of hub is analyzed. And sample selection of parameters is completed. On this basis, the hub fairing is designed and optimized by establishing surrogate model and solved by using optimization algorithm. Finally the optimum design method of drag reduction applied to coaxial rigid rotor hub has been built. And the correctness of optimum design method of drag reduction applied to coaxial rigid rotor hub is verified by comparing results of computational fluid dynamics(CFD), wind tunnel test and optimum design, which is less than 2%.