The invention discloses a fault detection device for LED traffic lights. The device is mainly composed of a working condition detection module (7), a signal switching detection module (6), a microcontroller (8) and a communication module (9), wherein the microcontroller (8) can carry out time synchronization with a signal controller of the LED traffic lights (1) through the signal switching detection module (6). The microcontroller extracts and stores correct working condition characteristics of the traffic lights under a learning mode, and carries out fault detection on the traffic lights through the working condition detection module (7) with 1 second as a cycle under a monitoring mode, capable of detecting faults of power-off, power-on, lattice deletion, messy code, color conflict, timing error of a full screen light, an arrow light, and a countdown light as well as state conflict of different traffic phases at a same intersection and the like. The device provided in the invention can send various real-time fault information of the LED traffic lights to a management centre, conductive to timely maintenance and prevention of faults of the whole traffic lights, thereby guaranteeing safe, orderly and smooth traffic.