In order to solve the problem of yaw control for unmanned helicopter, the yaw control law design technique based on frequency domain identification method is discussed. According to the principle of counterweight balance, the comprehensive model of yaw channel is established based on using sweep frequency fly test for frequency domain identification. The yaw control law design technology are proposed, the control parameters are ascertained, optimized and verified. The simulation results show that the technology can realize the mathematical modeling and control law design of unmanned helicopter, which has better control quality and engineering value.