The paper introduces composition and principle of ground current online monitoring system of high voltage cable metal sheath from hardware structure and software design. The system integrated application of a variety of techniques to achieve Large current sampling and Temperature sampling, GPRS data transfer, SQL server data storage, Web data display and threshold alarm function. The system has been successfully developed, it provides a new, efficient, stable, low-cost method for cable metal sheath ground current monitoring, the system has good prospects of application.