Abstract: A method for optimizing pipe wall thickness considering location class upgrading was provided, which aims to solve the problem of unacceptable risks caused by location class upgrading in the later stage of natural gas pipeline operation.Specifically, this method was to ensure that the pipeline risks of all location classes can satisfy the requirements for social risks through quantitative calculation of reliability degree according to the Reliability-Based Design and Assessment(RBDA)method, and it was also to realize the economic optimization of pipelines for choosing reasonable pipe wall thickness by lifecycle cost comparison. As a case study, this method was used to calculate a pipeline with diameter of 508 mm. Moreover, the effects of location class upgrading time, location class, and pipe diameter on the optimal wall thickness of the pipeline were discussed. According to the research results, the optimal wall thickness of pipeline increases with the increasing of location class upgrading time, location class, and pipe diameter. Compared with RBDA method, this method is more comprehensive, capable of minimizing the economic cost, and maximizing the pipeline safety. However, this method cannot be used to predict the location class upgrading in the future. Thus, further study is required.