Generator sets are typical rotary machines and the movements of each part of them have cyclic variation. When there are some faults in generator sets , the vibration signal of sets has a cyclostationary feature. The nonstationari ty always changs with the faults. So, the degree of cyclostation was proposed to monitor and analyze the fault trend of generator sets by using the thirdorder cyclic moment and binary decision method .The method can reflect the state of fa ult and suppress the noise and interference. It can be used as the fault feature vector to analyze trend of the fault development. The result is better than the analysis result of using traditional vibration amplitude and intensity .