Due　to　the　status　quo　of　lack　of　data　about　high-tensile　steel　in　H2S　environment,　the　fatigue　crack　growth　rate　of　4130X　steel　used　in　compressed　H2S　vessel　was　investigated.　Considering　its　practical　operating　ambient　and　stress　condition,　after　overcoming　enormous　difficulties,　the　self-modified　WOL(wedge-opening-loading)　specimens　were　used　in　the　specifically　designed　low-cycle　corrosion　fatigue　testing　machine,　in　order　to　complete　the　tests　under　0.0067　Hz,　in　saturated　H2S,　moderate　concentration　and　air　environment,　respectively.　Moreover,　the　mathematical　expression　of　da/dN-ΔK　was　concluded　by　the　fitted　curve　using　Paris　formula.　Contrast　study　between　the　changes　of　the　specimens＇　microscopic　fracture　and　the　stress　intensity　factor　K　was　conducted.　Therefore,　the　quantitive　result　of　K　of　three　stages　in　different　environment　was　determined.　The　results　show　that:　1)　da/dN　in　H2S　environment　is　above　20　times　of　that　in　air　environment.　2)　when　the　concentration　of　H2S　reaches　to　a　certain　range,　its　effect　on　da/dN　is　not　scaled　up.　da/dN　differs　by　2.4　times　while　the　concentration　differs　by　11　times.　The　corrosion　medium　accelerates　the　fatigue　failure.