Abstract: In view of problem that current underground explosion-proof computer has no monitoring function for electric quantity of battery, a design scheme of electric quantity of battery monitoring system of underground explosion-proof computer based on USB protocol was proposed. In the system, small single-chip microcomputer with AD conversion is used to collect and process electric quantity of battery, the collected data is transmitted to module of USB to serial port，then sampling value of electric quantity of battery can be got by upper computer through virtual serial port. The test result showed that the indexes of the system accord with working time of load, data transmission has higher reliability and relative error of AD conversion can meet with demands of collection of electric quantity of battery.