An activated carbon (AC) electrode-based capacitor soft-pack was incorporated into a gas bag, and the gases, if produced during the charge and discharge of the capacitor, can be online analyzed by Gas chromatography. This method is effective to test the stability of capacitors using PC-based organic electrolytes up to 4 V. The kinetics of gas production was obtained and the components of the gases were analyzed quantitatively. Salts in the organic electrolyte were firstly decomposed, rather than the solvent, under the conditions of less water and AC with few functional groups. It provided new insight into understanding the stability of capacitors in high potential.