The invention relates to a GIS mechanical fault live detection system based on acoustic imaging. The system comprises a sound intensity measuring unit, an acquisition module and a test host which aresuccessively connected. The sound intensity measuring unit comprises a semicircular metal rack. The semicircular metal rack is provided with five groups of sound intensity probes along a circumferencedirection. Each group of sound intensity probe is a P-P type sound intensity probe formed by two sound intensity microphone sensors. After trial, through using the method of the invention, a state ofan operated GIS device can be assessed and fault diagnosis can be given.