Abstract: The coupling of the pre-stressed thermal insulated tubing string broke down inside the steam flooding wells, after the tubing were used in high temperature and high pressure steam for about two years. With further check, it was found that most of the weld joints between the inner and outer tubing also cracked. The failure analysis for the accidents has been carried out by the analysis of chemical composition for the steels, microstructure observation, mechanical property tests, and the investigation of the service environment etc.. The results show that the early damage of the pre-stressed thermal insulated tubing string is mainly induced by the caustic stress corrosion, which can be strengthened by an unstable microstructure of the coupling serviced at high temperature for a long time. Moreover, the high pre-stress design on the thermal insulated pipe for the cyclic steam injection may be not suitable to the situation of steam flooding, which would result in the weld joint cracking.