The safety of the pipeline in use is tightly linked with the resident life and belongings. Reliable structural integrity and safety of gas pipelines under various service pressure events including defects should be warily evaluated. The reliability evaluation of gas pipelines is necessary to prevent risk. In this paper, Markov chain Monte Carlo is proposed to analyze the reliability of factors affecting gas pipeline operational condition in consideration of the character of historical data, the calculating processes of reliability prediction are provided in view of performance degradation characteristics of the factors.This paper takes corrosion as important factor affecting pipeline operation for example, calculates the reliability indexes of gas pipeline, studies the relation of failure rate and length/depth of corrosion pit ,operation time,etc. seeks weak links of system, and brings forward concrete and reliable measures to improve system reliability.