The　acoustic　emission　signals　of　fatigue　crack　propagation　in　Q345R,　which　is　the　typical　representative　of　common　steel　for　pressure　vessels,　were　investigated　in　detail　to　construct　a　relationship　between　fatigue　and　acoustic　emission.　The　results　show　that　there　are　three　distinct　stages　of　acoustic　emission　during　fatigue　crack　propagation　in　Q345R.　Cumulative　count　and　cumulative　energy　can　characterize　the　whole　fatigue　crack　propagation　well.　The　transition　from　the　2nd　stage　to　the　3rd　stage　of　acoustic　emission　advances　that　of　linear　elastic　fracture　mechanics,　indicating　that　acoustic　emission　is　more　sensitive　to　the　unstable　fracture　stage　of　fatigue　crack　propagation.　The　relations　of　count　rate　and　energy　rate　to　fatigue　crack　propagation　rate　of　Q345R　are　established　respectively　for　predicting　the　remaining　life　of　Q345R.　©　All　right　reserved.