With　a　quantitative　analysis,　the　probability　importance　and　the　criticality　importance　of　the　basic　events　of　the　fault　tree　were　calculated,　and　the　failure　probability　of　top　events　was　determined　for　the　pipeline.　The　steel　pipe　quality,　weld　quality,　installation　quality,　material　selection,　mechanical　damage,　and　operator　quality　were　the　major　factors　to　affect　the　safety　and　reliability　of　gas　pipelines.　The　computer　software　was　developed　for　the　fault　tree　analysis　of　long　gas　transmission　pipelines.