Gas insulated switchgear (GIS) is widely used in the construction of State Grid Substations, and it is usually necessary to do insulation withstand voltage tests before GIS is put into production. To locate faulty equipment on site, according to the practical application environment, a fast and effective method was presented to locate the fault equipment in GIS insulation withstand voltage test by using distributed acoustic sensing (DAS) system. Through the back Rayleigh scattering signal of the optical fiber itself, the phase heterodyne was adopted phase-sensitive optical time-domain reflectometer (φ-OTDR) multi wavelength multi path modulation and demodulation method, which can visually and real-time monitor the optical fiber vibration signals at different positions of the metal shell of the GIS system to reduce the test blind spots. The experimental test results show that, fast and accurate positioning of fault equipment in GIS can be realized with the developed DAS system, and the positioning accuracy can reach within 3 m. It has a good reference value for timely troubleshooting and maintenance of GIS field faults and ensuring the safe operation of power equipment.