For　the　metal　plate　structure　in　micro　crack　detection　problem,　the　thesis　of　the　second　harmonic　of　the　nonlinear　Lamb　wave　detection　method　research　based　on.　First,　the　board　in　the　second　harmonic　nonlinear　Lamb　wave　theory　is　used　to　study,　analyses　the　influence　of　the　micro　crack　width　and　length　of　second　harmonic　excitation　efficiency,　and　through　the　numerical　simulation　of　nonlinear　effect　of　different　length　and　width　of　the　micro　crack　and　the　Lamb　wave　interaction.　The　results　show　that　with　the　increase　of　micro　crack　length,　the　two　harmonic　amplitude　increases　and　the　two　harmonic　amplitude　decreases　with　the　increase　of　the　micro　crack　width.　Based　on　the　above　research,　the　plate　crack　in　nonlinear　Lamb　wave　detection　experiments.　The　results　show　that　by　measuring　structure　of　Lamb　wave　second　harmonic　nonlinearity　coefficient,　for　structure　of　micro　crack　detection　and　quantitative　evaluation.　The　research　work　is　a　useful　exploration　for　the　quantitative　detection　of　micro　cracks　in　the　plate.　©　2017　Journal　of　Mechanical　Engineering.