A nonlinear flight dynamics model is established for unmanned helicopter real-time simulation. As an example, the flight control law for an unmanned helicopter is designed. Hardware-in-loop simulation of hover maneuver flight and low speed flight is conducted, and the simulation results are compared with the flight test data. The simulation results agree well with the flight test data, thus proving the accuracy of nonlinear flight dynamics model. The attitude is controlled well during flight, and the rationality of control parameters is proved.