Objective To conduct failure analysis of organic coating under high temperature, high pressure condition of natural gas well, so as to provide suggestions for the selection of the organic coating used in the natural gas well pipes. Methods In this paper, the downhole condition of natural gas well containing media such as CO2 and H2S was simulated and the long-term immersion experiment of 9 rounds lasting 1914 h was conducted to compare and test the thickness, impact toughness and other mechanic parameters of organic coatings. Macroscopic and microcosmic changes of immersion surface were observed and analyzed. Results Organic coatings aged slowly after repeated pressure increasing and decompression in the rigorous indoor test. The wear resistant value decreased from the initial 3. 28 L / μm down to around 2 L / μm. The hardness value decreased from the initial 125 to about 95. The impact toughness dropped from the initial 37. 6 J to about 23. 5 J at 890 hours of immersion, then tended to be stable. After 1914 hours, the connect property between coating and carbon steel matrix turned worse, and obvious local pitting corrosion was found on the coating surface. Conclusion Failure characters which occurred in the indoor coating test were similar with those in the field production of pipe coating in gas well field. The failure process was weight loss, less thickness—blister—corrosion under polymer layer, and then peeling off. In order to avoid the failure of internal coating of oil pipe and to improve the corrosion protection effect, it is recommended to control the degree of cure in oil production and processing process so as to reduce the coating defects caused by low degree of cure, avoid potential damage of coating which is due to wire operation and rapid pressure releasing in engineering operation, and inject corrosion inhibitor regularly to reduce corrosion.