To verify the rationality of PSS placement and effect of suppressing low frequency oscillation,the IEEE-57 test system was selected to analyze the oscillation mode and damping characteristics.SAPSO algorithm was used to coordinately optimize PSS parameters in 3 steps in the test system.Firstly,PSS parameters of No.15 were optimized in single machine infinity system.Then,the No.18 generator was placed and configured with one PSS whose parameters were also optimized to improve the damping ratio of the test system.In addition,PSS parameters of No.15 and No.18 were optimized coordinately to obtain higher damping.The results of time-domain simulation under small disturbances and Prony analysis demonstrates that,the damping effect of coordinately optimized PSS parameters is better and the method of coordinated optimization and placement is feasible and available.