In order to timely and accurately grasp the data of operation condition, construction quality, traffic safety, vehicle location, equipment failure data of operation site large maintenance machinery, and realize the rapid diagnosis and process of alarm fault occurred in the field, it was urgent to develop a set of large-scale maintenance machinery state monitoring and fault diagnosis system to meet the needs of users. With installing a monitoring and diagnosis device based on the vehicle electric control system, all kinds of information collected at the scene after the corresponding treatment was sent to the ground terminal processing system by 4G wireless module, which realized vehicle on-line monitoring and fault diagnosis. The system has been successfully applied in a variety of the large maintenance machinery, and achieved good application effect.