In　view　of　insufficiency　in　crack　growth　threshold　measurement　technology,　the　survey-point　displacement　of　specimen　and　test-load　are　collected　through　digital　measurement　technology,　and　the　crack　size　is　calculated　through　the　compliance　method,　the　cycle　index　is　recorded　according　to　the　wave　crest　of　survey-point　displacement.　Besides,　the　integrated　objective　of　test　control,　data　collection,　monitoring　and　processing　are　implemented　by　the　multi-thread　software.　The　results　of　the　fatigue　crack　growth　thresholds　of　steel　40CrNiMo,　which　are　obtained　from　group　test　method　under　different　load-ratio,　prove　the　reliability　and　feasibility　of　measuring　and　testing　techniques.　©　2017,　Editorial　Department　of　Journal　of　Beijing　Jiaotong　University.　All　right　reserved.