In this paper, the flight control system for a small size unmanned helicopter is discussed. The system is mainly used as a platform for the research of autonomous flight controller. So the modularity and expansibility is preferred. Firstly, the hardware of the system are designed based on DSP and FPGA. Then the function modules of FPGA is provided, which are designed to ensure the system's expansibility. Finally, the software scheme of the flight controller is presented. This system is very lightweight and low cost. Besides, it provided exoteric system interface for further development.