The design conception and operating principle of PSS4B power system stabilizer are presented, the advantage of PSS4B's low frequency oscillation suppression ability is verified by theoretical analysis and comparison with PSS2B. After that, this paper puts forward an improved PSS model named PSS4B-W based on the existing problems on PSS4B’s engineering application. PSS4B-W phase modulation method is proposed by generator excitation system’s no compensation frequency response test, and the phase modulation effect is verified by generator load voltage step test. The step test result shows that PSS4B-W can not only meet the requirements of high frequency band’s phase modulation, but also provide better suppression effect on low frequency band. Finally, this paper summarizes and presents the recommendations and advices of PSS4B and PSS4B-W’s engineering application.