Abstract: Power output optimization of wind farm becomes an urgent problem to be solved during wind farm is planned and designed. In this paper, the mathematical model for power output optimization of wind farm under transient stability constraints is put forward, and the objective function and constraint criteria are defined. Based on the transient stability margin sensitivity of wind power output, influence of different wind farm on power system transient stability is analyzed, and the power output optimization algorithm of wind farms is put forward. In the end, the simulation based on PSASP verifies the effectiveness of the algorithm proposed in this paper.