Contraposed　to　the　lack　of　testing　and　evaluation　standards　of　high-pressure　compressed　natural　gas　(CNG)　vessels,　using　fracture　mechanics　approach　and　probability　analysis　method,　H2S　stress　corrosion　cracking　tests　and　corrosion　fatigue　tests　were　done　in　the　H2S　solution　of　moderate　concentration　and　at　a　low　frequency　6.7　μHz.　The　relations　between　fatigue　crack　growth　rate　da/dN　and　the　increment　of　fracture　toughness　ΔK　were　determined.　By　using　inverse　inferring　method,　considering　critical　crack　sizes　of　H2S　stress　corrosion　cracking,　crack　increments　of　corrosion　fatigue,　random　capability　and　reliability　of　data　and　the　practicality　of　different　service　period,　the　allowable　crack　sizes　of　different　service　period　were　calculated　and　the　curves　between　allowable　crack　depth　and　original　crack　length　were　obtained,　which　would　supply　more　accurate　data　to　determine　the　service　period　and　to　evaluate　pressure　vessels＇　residual　life.