Abstract: Self-ignition of ferrous sulfide has occurred frequently on the 2nd West-to-East Gas Pipeline. In order to diagnose key sulfide-generated points/parts on the west section of this pipeline and take proper preventive measures, Chandler chilledmirror dew-point hygrometers and multi EA5000 elemental analyzer are used to test and analyze the gas samples and pigging products gathered along the west section. The variations of water and H₂S contents of natural gas and of H₂S content of pigging products are obtained. Combing the morphology and tested total sulfur content of pigging products, internal inspection data and elevation changes along the pipeline, criteria for diagnosis of key sulfide-generated points/parts is formed, key station points and pipe parts are determined, and related preventive measures are formulated.