Proposed in this paper is a new conjugate gradient approach for the coordination of the power system stabilizer ( PSS) parameter optimization of multi-machine power system. In this approach,combination functional index is introduced as a performance index to evaluate the damping effect of PSS,the integral term of the index is dealt with by means of the variational method,and a backward trajectory integration approach is put forward to calculate the gradient of the index to the PSS parameter vector. Moreover,minimizing the index is taken as the objective function of the optimization model of the PSS parameter,and the objective function considers the nonlinear features of big disturbance of the power system,so that the optimized PSS can improve the small-disturbance stability of the power system and efficiently damp the power oscillation caused by large disturbances. In addition,the practicality and effectiveness of the proposed method are verified on IEEE 4-generator 2-area and IEEE 10-generator New England test systems.