The voice gateway mainly completes the interconnection between IP communication system and external analog circuit, which is major equipment for the command and very important to the command of the army. Currently, we can repair only after the system can not work normally. In this paper, a method of forecasting failure is proposed, which monitors the differential value of the actual value and the theory value.Then replace the actual value with the Grey-forecasting model. According to the simulation results, Grey-forecasting model is better in used.