The invention provides an underground cable fault detection robot. The underground cable fault detection robot comprises a robot body, a driving device for driving the robot body to travel, a cradle head, a lifting mechanism, a CCD camera and an LED lamp, wherein the lifting mechanism is disposed on the robot body and drives the cradle head to lift, the cradle head is connected with the CCD camerafor controlling the CCD camera to swing, and the LED lamp nears to the CCD camera. The underground cable fault detection robot has the advantages that the underground cable fault detection robot canbe used for cable detection under narrow and dark ground in place of labors, and a height sensor, an angle sensor and a control module can be used for guaranteeing a shooting angle; a built-in image processing module is capable of finding fault points by processing images automatically and feeding the fault points back to a master power grid server through a wireless module. A method with specificsteps for image processing is provide and is effectively applicable to underground dark features so as to position faults precisely, effectively and extensively.