In order to solve the difficulties in flight control law design of a helicopter caused by its strong coupling characteristics， an improved linear quadratic regulator （LQR） design method based on particle swarm optimization algorithm is proposed. Based on the linearized state space model of a helicopter， a basic algorithm to solve the full state feedback matrix in helicopter flight control law is established based on LQR design method. A cost function for particle swarm optimization， which maximizes the influence factor of main state feedback coefficients and takes the stability of the system as constraint， is designed. The multi-parameter synchronous optimization of weighting matrix Q is implemented， and the optimized main state feedback coefficients are used as control law design results of a helicopter. The flight control law of a UH-60A helicopter at hover state is designed and verified. The results show that the control law designed by using this method has good performance and the flying quality of the helicopter is increased considerably. Meanwhile， the difficulty in determining weighting matrix during LQR design procedure is solved systematically based on the optimization method developed in this paper， and the efficiency in control law design is increased.