The invention provides an alarm system for detecting the abnormal operation of a wind driven generator. A sound acquisition module is disposed on the wind driven generator. The alarm system includes the sound acquisition module, an acoustic signal processing module, a fault diagnosis module, and an early warning module which are successively connected. The early warning module is configured to detect the working state of the wind driven generator. If discovering that the wind driven generator operates abnormally, the early warning module gives an early warning message to remind a maintenance worker to perform maintenance. The alarm system provides a simple, high-efficiency and low-cost noncontact in-position fault diagnosis method for anomaly detection of the wind driven generator, and gives guidelines for the normal operation and maintenance of the wind driven generator.