Aiming at the disadvantage that the data transmission through RS-422 serial port needs a long period because the large amount of partial discharge signal data are collected by the distributed sensors for detection of GIS (Gas Insulated Switchgear) partial discharge, a maximum data compression algorithm is adopted in the on-line monitoring system of GIS partial discharge based on distributed sensors in this paper. By the proposed algorithm, a large number of real-time high-speed data collected by A/D can be transmitted to the background monitoring system effectively, therefore the bottleneck problem of the data transmission is solved. The experimental verification shows that the proposed data transmission mode of the system is fast, safe and reliable with a good practicability.