A　real-time　measurement　method　for　the　thread　number　of　rail　fastener　is　proposed.　The　measurement　is　achieved　by　the　processing　of　thread　images.　After　analysis,　the　fastener　thread　has　the　elliptical　feature,　so　two　parameters　-　-elliptical　similarity　and　elliptical　integrity　are　proposed.　Based　on　the　two　parameters,　the　thread　region　is　located.　Combining　with　the　light　intensity　distribution　of　thread　region　and　thread　positions,　the　thread　number　is　measured.　200　samples　are　chosen　to　verify　the　validity　of　this　method.　Experimental　data　show　that　the　limitation　error　of　this　method　can　reach　0.1985　threads.　©　2020　IEEE.