Abstract: In order to resolve the autonomous flying control problem of a small unmanned helicopter, a design method for fast-optimization robust H_∞ controller is presented based on helicopter hovering model, and a double-closed-loop flying controller based on reduced-order observer is designed. The inner-loop controller uses H_∞ robust technology for helicopter flight attitude control, and the outer-loop controller uses PD (proportional-derivative) technology for the helicopter displacement control. The proposed controller is applied to the flight control system of an independently developed miniature helicopter, and the fully autonomous fixed-point hovering flight is realized in interference environment. Experiments demonstrate the effectiveness and robustness of the proposed control approach.