Abstract: In view of problem that industrial Ethernet switch has higher requirement to quality of power supply, a constant supply system for industrial Ethernet switch was designed. Hardware circuits of the system were introduced in details, namely DC stable voltage supply circuit, charging management and control circuit of battery, temperature detection circuit of battery, switching circuit of power supply, CAN bus communication circuit and single-chip microcomputer control circuit, and main program flow of the system was gave. The test result showed that the system can meet with supply requirements of industrial Ethernet switch under complex environment with characteristics of quick dynamic response, low static power consumption.