The invention relates to an online state monitoring and fault diagnosis device and an online state monitoring and fault diagnosis method for a rotary machine. The device comprises a data acquisition device 101, a feature extraction device 102, a data management device 103, a display device 106, a device 107 such as a mouse, a keyboard or the like for setting parameters and managing equipment by a user, a multi-model detector training device 104, and a multi-model fault diagnosis device 105. The method comprises the following steps of: acquiring signals by using the data acquisition device; storing the signals, and extracting features of the signals by using the standard feature array extraction device; training a detector by using the training device for the detector for identification; performing identification by adopting the trained hybrid model detector; and outputting and recording the identification result. The device and the method can diagnose common rotary machine faults such as shaft eccentricity, bearing eccentricity, rolling body abrasion and the like, and have the advantages of high automation degree, capability of identifying multiple fault types, capability of realizing early diagnosis, good fault database expansibility and the like.