Fatigue　cracks　evaluation　is　mainly　based　on　qualitative　evaluation,　and　quantitative　evaluation　is　still　in　the　primary　stage.　In　quantitative　evaluation　investigations　thermal　fatigue　damage　factor,　D,　expressed　in　terms　of　the　percentage　of　surface　crack　area　(S)　and　the　average　width　of　surface　main　crack　(Ws),　are　difficult　to　calculate　accurately.　Therefore,　combining　scanning　electron　microscope　images　and　Photoshop　software,　we　calculate　the　conversion　rate　between　the　pixels　and　the　actual　length　of　scale,　then,　cracks　parameters　are　expressed　in　pixels.　Eventually,　the　thermal　fatigue　damage　factor　can　be　represented　by　pixels,　and　an　accurate　thermal　fatigue　damage　factor　was　calculated.　Fatigue　cracks　can　be　comprehensively　and　quantitatively　evaluated.　(C)　2019　Elsevier　B.V.　All　rights　reserved.