An underwater robot driving motor failure gray prediction device is arranged on an underwater robot body and connected with the underwater robot body. The prediction device comprises a vibration displacement signal sensor for measuring vibration displacement of a motor and outputting voltage signals, and a displacement signal sampling conditioner connected with a vibration displacement signal sensor circuit and a failure pre-measuring device. The vibration displacement signal sensor is fixed on a driving motor of the underwater robot body, and the failure prediction device is connected with the displacement signal sampling conditioner through a 232 serial port, receives vibration displacement signals and analyzes and predicts future time vibration signals. The underwater robot driving motor failure gray prediction device has the advantages that the prediction device solves the problems that in the prior art, underwater robot driving motor failures can not be predicted to cause incapability of underwater work of an underwater robot.