The　assessment　of　fatigue　crack　propagation　of　steel　structures　is　essential　and　important　especially　to　improve　the　application　of　high　strength　steel　in　construction.　The　load　ratio　R,　reflecting　mean　stress　effects,　will　be　changed　with　crack　extension　in　the　steel　structures　with　complicated　geometry.　In　this　paper,　the　Walker　equation　is　employed　to　fit　the　fatigue　crack　propagation　rate　of　steel　grades　S355　and　S690　based　on　experimental　data　in　the　literature　to　incorporate　the　mean　stress　effects.　The　material　fatigue　crack　propagation　parameters　with　95%,　97.7%,　and　99%　guarantee　of　Walker　equation　were　obtained　by　a　stochastic　analysis　using　the　Monte　Carlo　method.　The　fatigue　life　was　firstly　predicted　by　the　analytical　method　and　was　used　as　a　baseline　for　numerical　fatigue　crack　propagation　simulation.　A　user-defined　fatigue　crack　propagation　subroutine　based　on　the　Walker　equation　was　developed　using　phantom　nodes-based　extended　finite　element　method　(PN-XFEM)　and　Virtual　Crack　Closure　Technique　(VCCT)　to　consider　the　mean　stress　effects.　The　proposed　three-dimensional　fatigue　crack　propagation　simulation　subroutine　is　successfully　validated　of　both　steel　grades,　S355　and　S690.　©　2020　The　Authors