Er-containing　Al-Mg　alloy　plates　were　processed　by　different　heating　treatments.　The　effects　of　microstructure　on　fatigue　crack　propagation　of　the　plates　were　analyzed.　The　results　show　that　the　smaller　the　length/diameter　ratio　of　the　grain,　the　slower　the　fatigue　crack　propagation　rate;　with　the　reduction　of　fatigue　crack　propagation　rate,　the　crack　width　increases,　while　the　crack　path　twists　and　turns.　Due　to　the　addition　of　rare　earth　element　Er,　Al-3(Er,　Zr)　particles　are　formed　in　the　alloy,　and　they　pin　the　dislocation　strongly,　hinder　dislocation　motion,　and　reduce　the　stress　concentration　in　the　grain　boundary　produced　by　the　dislocation　pile-up,　thus　reducing　the　fatigue　crack　growth　rate.