Long　distance　pipeline　transmission　is　considered　to　be　the　most　economic　and　safest　method　to　transport　natural　gas　nowadays　and　pipeline　safety　problem　is　a　focus　of　concern　in　the　academic　and　industrial　circles.　Pressure　fluctuation　and　corrosive　environment　can　make　the　typical　working　condition　of　long　distance　pipeline　become　a　low　frequency　corrosion　fatigue　condition,　which　leads　to　high　risk.　In　this　paper,　mathematic　model　of　fatigue　crack　growth　rate　(FCGR)　considering　frequency　and　stress　ratio　has　been　developed　and　the　expressions　of　every　parameter　were　fitted.　Critical　stress　intensity　factor　(K(ISCC))　in　H(2)S　saturated　environment　(2300ppm)　was　measured.　In　view　of　the　operating　condition　and　applied　stress　of　pipeline,　low　frequency,　high　stress　ratio　corrosion　fatigue　tests　of　X70　base　metal　were　carried　out　in　H(2)S　saturated　and　air　environments　respectively.　According　to　the　ASME　BPVC　Section　XI,　by　using　inverse　inferring　method,　considering　critical　crack　sizes　of　H(2)S　stress　corrosion　cracking,　crack　increments　of　corrosion　fatigue　and　different　service　periods,　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　West-East　natural　gas　transmission　pipeline＇s　residual　life.