The invention relates to a status monitoring and diagnosing device of an electrical system of maintenance machinery, which comprises an electrical control system for the operation of the maintenance machinery, a diagnosing host, a CAN bus interface composed of an AVR singlechip and a CAN controller, an RAM with double ports and an A/D converter; a main CPU of a program control motherboard is connected with the AVR singlechip of the CAN bus interface by the RAM with double ports which realizes data exchange; the A/D converter is connected between a digital signal input end of a singlechip of a40-way display board and an analog signal output end of a 40-way selection switch of the 40-way display board; the main CPU of the electrical control system for the operation of the maintenance machinery is connected with a diagnosing host carrying data collection, analysis and diagnosing programs by an RS232 interface. By communicating with a program control host of the maintenance machinery andthe 40-way display board, the diagnosing host obtains program control signals and analog control signals, analyzes and finds out abnormality and realizes the purpose of diagnosing the electrical system of the maintenance machinery.