Abstract: The failure probability assessment (FPA) is one of the key quantitative risk assessments on gas pipes. The present paper analyzed both advantages and disadvantages of the subjective FPA method based on experts experience and the objective FPA method based on historical failure data or intensity theory, respectively. A new assessment method combined by the both subjective and objective methods was developed in this paper, and it adopted a statistic analysis on historical failure data to calculate an average failure probability of gas pipes and applied a hierarchy analysis on experts evaluation data to figure out a failure possibility of gas pipes. A relationship between the subjective failure possibility and objective failure probability was built up through this integrated analysis method that assumes the medium possibility of the subjective assessment equal to the average failure probability of the historical failure data. Taking the failure probability by corrosion on buried steel pipelines as an example, the paper expatiated upon this approach of the failure probability assessment, which firstly estimated the failure possibility of pipelines under any conditions via the subjective assessment, and then determined the objective failure probability of pipelines by means of the relationship between the subjective possibility and objective probability.