This　paper　focuses　on　the　derivation　of　the　aerodynamic　force　for　the　cantilever　plate　in　subsonic　flow.　For　the　first　time,　a　new　analytical　expression　of　the　quasi-steady　aerodynamic　force　related　to　the　velocity　and　the　deformation　for　the　high-aspect-ratio　cantilever　plate　in　subsonic　flow　is　derived　by　utilizing　the　subsonic　thin　airfoil　theory　and　Kutta-Joukowski　theory.　Results　show　that　aerodynamic　force　distribution　obtained　theoretically　is　consistent　with　that　calculated　by　ANSYS　FLUENT.　Based　on　the　first-order　shear　deformation　and　von　Karman　nonlinear　geometric　relationship,　nonlinear　partial　differential　dynamical　equations　of　the　high-aspect-ratio　plate　subjected　to　the　aerodynamic　force　are　established　by　using　Hamilton＇s　principle.　Galerkin　approach　is　applied　to　discretize　the　governing　equations　to　ordinary　differential　equations.　Numerical　simulation　is　utilized　to　investigate　the　relation　between　the　critical　flutter　velocity　and　some　parameters　of　the　system.　Results　show　that　when　the　inflow　velocity　reaches　the　critical　value,　limit　cycle　oscillation　occurs.　The　aspect　ratio,　the　thickness,　and　the　air　damping　have　significant　impact　on　the　critical　flutter　velocity　of　the　thin　plate.