Abstract: A leakage accident occurred in a underground coalbed methane pipeline. The causes of pipeline leakage were analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, mechanical property testing, X-ray diffraction analysis, scanning electron microscopy and energy spectrum analysis, and external anti-corrosion coating performance testing. The results show that the 3PE anti-corrosion layer on the outer surface of the pipeline was brittle and cracked, and the outer surface of the pipeline without the protection of the external anti-corrosion layer came into direct contact with the soil electrolyte, causing severe wall thickness corrosion and thinning. The medium inside the pipeline contains substances such as water, H₂S, and CO₂, which caused uniform corrosion on the inner surface of the pipeline and local corrosion at the bottom of the pipeline, ultimately led to pipeline leakage.