A sulfur hexafluoride discharge decomposition gas component analysis system is composed of a pressure adjuster console 1, an insulation transformer 2, a non-blooming test transformer 3, a non-local-discharge protective resistance 4, a capacitor bleeder 5, a sulfur hexafluoride discharge decompose device 6, a non-inductive check resistance 7, a match resistance 8, an oscillometer 9, and a gas spectrometer 10. And the method comprises that (1), using a vacuum pump 18 to vacuum the sulfur hexafluoride discharge decompose device 6, (2), using an inlet needle valve 17 to feed SF6 gas into the sulfur hexafluoride discharge decompose device 6, (3), measuring maximum external test voltage and initial PD voltage, (4), generating PD under different electrodes, (5), collecting gas, (6), analyzing gas components, (7), collecting PD pulse signal wave shape, diagnosing accident and recognizing mode. The invention has wide application in research, teach, academy and industry, used in theory analysis and research of PD online state check of GIS device.