Abstract: To address the problems of high risks and long construction periods when installing substation test fixtures on gas insulated switchgear (GIS) chambers for withstand voltage tests of 110 kV cable lines with GIS terminals on both sides before operation, a dedicated sleeve device for external withstand voltage test of 110 kV cable GIS terminals was developed. Connection method and compact structure for withstand voltage test outside the chamber were designed, and performance of the device was verified through simulation calculations and experiments. It was successfully applied to the production site. Results showed that compared with traditional devices, the device had the advantages of compact and flexible structure, green environmental protection, convenient operation, strong adaptability, and strong universality, with extremely high promotion and application value. It solved the problem that high voltage cable GIS terminals could not be tested separately outside the chamber, simplified operation process, effectively reduced construction risks, significantly reduced the duration and cost of cable withstand voltage testing, and shortened the time for cable line power outage maintenance.