In this paper, we describe the dynamic model of a four-rotor mini rotorcraft, and present the hardware design of real-time embedded control system for small Unmanned Aerial Vehicles (SUAV). We improve the driver performance for Brushless Direct Current (BLDC) motor. In addition, the modular programming method is adopted in software design to carry out the computation of control law, data processing and correction output to get the results satisfied. Finally, we evaluate the performance of stable flight using this real-time embedded control system between two control strategies. It is shown by the experiments that this onboard embedded control system is stable and highly reliable with low cost.