In order to test the hardware and software system of a small-scale unmanned helicopter, a hardware-in-the-loop simulation system is designed and realized. This simulation system is based on VxWorks embedded operation system, with the dynamic model for the model helicopter to simulate the fight. With the Futaba remote control (RC) equipments and the pulse width modulation (PWM) wave collecting and sending module, we can do test on all the three kind of control mode: remote control by pilot; semi-automatic control by pilot; automatic fly, and the changing-over. With the ground control station, we can do simulation on flight missions and subjects. So we can have a test on all the hardware and software of almost by the simulation system.