Gas pipelines buried under urban streets bear the loads both from the inner operation pressure and the vehicles over the street. After long-term service, the pipelines become unstable and vulnerable, which threat the safety of the normal process of the production and living. Nowadays in China, a lot of gas pipelines in urban area have been in-service more than 20 years. It has practical significance to assess the reliability of pipelines and to repair the old pipelines which are nearly to fail. In the paper, a limit state function was established to calculate the reliability of the pipeline buried under street, which was based on the mechanic analysis. The circumferential stress and the axial stress were both taken into account. The reliability of a pipeline buried under the street was analyzed with a given case. After analyzing the material strength degradation and the corrosion of the sample, the reliability of the pipeline and its development tendency were determined. After long-term service, the reliability of the pipeline declines. The insertion method was employed to repair the pipeline, by which the downward trend of the reliability was mitigated. The service life of the pipeline could be extended to 52 years.