In　order　to　apply　the　eddy　current　method　to　nondestructive　test　of　the　surface　hardness　of　mould　steel,　the　correlationstudies　were　carried　out　from　both　experimental　method　and　the　sensitivity　analysis　of　sensor.　Firstly,　the　samples　of　45　steel　and　S136　steel　with　different　hardness　were　prepared　by　adopting　different　heat　treatment　processes,　and　the　relationship　curves　between　hardness　and　tempering　temperature　were　obtained.　Secondly,　the　eddy　current　test　system　was　used　to　test　all　the　samples,　and　the　impedance　amplitude　and　hardness　of　the　samples　were　analyzed.　The　results　show　that　good　linear　relation　between　the　impedance　amplitude　and　hardness　of　45　steel,　while　good　nonlinear　relation　between　the　impedance　amplitude　and　hardness　of　S136　steel,　Finally,　the　sensitivity　of　three　different　sensors　for　detecting　hardness　were　analyzed,　and　the　detection　sensitivity　was　higher　when　the　coil　inductance　was　larger.　Moreover,　electromagnetic　sensor　was　produced　and　the　relevant　test　platform　was　built.　The　hardness　of　45　steel　and　S136　steel　were　tested,　the　test　results　are　consistent　with　the　results　of　the　conventional　eddy　current　sensor.　The　reliability　of　test　methods　and　data　processing　method　are　verified.　The　above　studies　show　that　eddy　current　testing　can　characterize　the　mechanical　properties　of　mould　steel　fast　and　nondestructively,　and　the　eddy　current　testing　method　and　the　system　are　expected　to　be　applied　to　engineering　quality　testing.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.