The invention relates to a multi-region detection system for the partial discharge decomposition components of insulating gas and a method thereof, which belong to the technical field of on-line gas-insulated equipment insulation monitoring. The system comprises a voltage regulator, an isolation transformer, a corona-free test transformer, a partial discharge-free protective resistor, a capacitive divider, an insulating gas discharge decomposition device, an ultrahigh-frequency antenna, an oscillograph, a gas chromatograph-mass spectrometer and the like, and the insulating gas discharge decomposition device comprises a housing, insulating sleeves, connecting rods, electrodes, valves, a vacuum meter, a gas pressure meter, a vacuum pump, an SF6 gas bottle, a pure compressed air bottle and the like. The method utilizes the system to respectively detect the discharge decomposition components of multiple regions in the insulating gas discharge decomposition device. The invention can accurately detect the components and component contents of the decomposed gas of a main gas chamber, a glow discharge region and an electron drift region and provide a standard. The invention can be widely applied to the on-line monitoring of gas-insulated equipment insulation, in particular to the on-line monitoring of GIS (gas-insulated switchgear) insulation.