As　a　method　to　realize　the　defect　detection　in　beam　structure,　this　paper　constructs　an　EMAT-laser　detection　system　to　detect　the　notch　defect　in　an　aluminum　beam.　EMAT　is　designed　as　a　transmitter　to　generate　single　Lamb　wave　mode.　A　high　precision　laser　detector　is　used　as　a　receiver　to　obtain　the　received　signals.　The　defect　is　localized　and　quantified　with　the　help　of　space-frequency-wavenumber　analysis.　The　evaluated　depth　of　the　defect　is　2.006　mm,　while　the　actual　size　is　2　mm.　It　shows　good　agreement　between　the　evaluated　result　and　actual　size,　the　error　is　only　0.3%.　This　method　also　can　be　used　in　the　evaluation　of　defect　in　other　materials.　©　Published　under　licence　by　IOP　Publishing　Ltd.