A reference observer-based tracking control system is designed to achieve accurate trajectory tracking control in engineering application for an unmanned helicopter. According to the desired flight path, a real-time reference observer is developed to estimate the desired states and feed-forward control signals as the inputs of the tracking controller. Then the controller uses full-state feedback control method to realize trajectory tracking. A certain unmanned helicopter is chosen as the control plant, and the flight simulation is carried out in the typical maneuver of the helicopter. Simulation result shows the satisfactory performance of the system and the control approach is easy to be implemented in engineering for its simple algorithm.