Abstract: An anticorrosion plastic alloy composite pipe for oil gathering and transportation failed during service. Investigations were performed to identify the possible failure causes of the pipe. Composition and thermal analysis of inner plastic alloy and outer GRP resin were systematically studied by using FTIR, TG-DSC, VST, etc. Results reveal that additives in failed plastic alloy may have not been stirred enough before extrusion or the content of additives may exceed their normal range. The glass transition temperature of GRP resin was much lower than that stated in standard. Hence, the lower state of cure for resin as well as the higher resin content of GRP layer makes the outer GRP structural layer have a relatively lower mechanical property, giving rise to the final failure of the composite pipe after serving for a long time under the co-effect of the aging and corrosion