Towards　the　safety　operation　of　metal　plate　structure,　a　nonlinear　Lamb　wave　mixing　method　was　develop　for　fatigue　detection　in　metal　plates.　The　numerical　simulations　were　conducted　to　investigate　the　nonlinear　interaction　between　the　two　A0　Lamb　waves　and　the　material　nonlinearity.　The　results　show　that　two　collinear　A0　Lamb　waves　produce　a　sum　frequency　S0　wave　which　propagates　in　one　direction　at　the　damaged　structural　material,　and　the　amplitude　of　the　sum　frequency　wave　exhibit　a　cumulative　growth　effect　with　the　propagation　distance.　Co-linear　Lamb　wave　mixing　experiments　were　conducted　on　metal　plate　specimens　with　different　fatigue　levels.　The　results　showed　that　the　amplitude　of　sum　frequency　wave　showed　a　monotonic　increasing　trend　with　the　increase　of　fatigue　cycles　of　the　specimen,　and　the　proposed　Lamb　wave　mixing　technique　can　be　used　to　characterize　the　fatigue　degree　of　metal　plates.　The　research　provides　a　feasible　solution　for　fatigue　evaluation　in　metal　plates.　©　2022　Acta　Acustica.