In　view　of　the　fact　that　Lamb　waves　decay　slowly　during　propagation,　the　use　of　ultrasonic　Lamb　waves　for　stress　detection　of　thin　metal　plates　has　become　a　hot　research　method　at　home　and　abroad.　In　order　to　understand　the　relationship　between　the　propagation　characteristics　of　Lamb　waves　and　the　stress　of　thin　metal　plates,　this　paper　gives　the　dispersion　curve　of　aluminum　plate　under　different　stresses　of　unidirectional　load　according　to　the　calculation　formula　of　Lamb　wave　dispersion　in　isotropic　plate.　The　propagation　of　the　basic　mode　and　first-order　mode　of　Lamb　wave　and　stress　field　in　the　same　direction　are　analyzed.　According　to　the　calculation　results　of　the　dispersion　equation,　the　Lamb　wave　A1　mode　is　more　sensitive　to　speed　changes　than　other　modes,　and　the　first-order　modal　speed　closer　to　the　cutoff　frequency　changes　more　obviously.　The　experiment　of　unidirectional　stress　load　applying　to　a　6061-aluminum　plate　with　a　thickness　of　1mm　is　carried　out.　Considering　the　multi-modal　characteristics　of　piezoelectric　probe　excitation,　the　electromagnetic　ultrasonic　transducer　is　used　to　excite　single-mode　Lamb　wave.　Compared　with　the　phase　velocity　change　rates　of　the　basic　mode　and　the　first-order　mode,　the　wave　velocity　of　the　A1　mode　changes　obviously,　and　the　experimental　results　are　consistent　with　the　simulation　data,　which　can　provide　an　important　basis　for　the　subsequent　stress　detection　of　thin　metal　plates.　©　2021,　Electrical　Technology　Press　Co.　Ltd.　All　right　reserved.