The invention discloses a GIS air leakage fault diagnosis system and method. The system comprises a temperature sensor, an air pressure sensor, a distributed capacitance measurement module, a signal conditioning circuit, an AD sampler, a controller and an alarm module. The temperature sensor, the air pressure sensor and the distributed capacitance measurement module respectively acquire environment temperature signals, air pressure signals in an air chamber and distributed capacitance signals between an air chamber conductive rod and a shell and transmit the signals to the signal conditioning circuit. The AD sampler samples the signals through signal conditioning and transmits the signals to the controller. The controller judges air leakage of the GIS air chamber according to the received signals and controls working of the alarm module according to the judgment result. The defects in the existing air leakage fault diagnosis technology of the GIS air chamber can be overcome and interference of environment temperature on air leakage fault diagnosis of the GIS air chamber can be eliminated.