To　establish　the　dynamical　model　of　piezoelectric　energy　harvester　with　magnetic　coupling,　the　modeling　approach　for　the　harvester　is　proposed　based　on　nonlinear　polynomial　description　of　nonlinear　restoring　force.　The　nonlinear　restoring　force　of　the　cantilever　beam　being　in　different　positions　is　measured　directly　by　a　small　electronic　dynamometer　and　the　polynomial　parameters　of　the　force　are　estimated.　Then　the　nonlinear　restoring　force　is　taken　into　account　to　establish　the　nonlinear　model　following　Hamilton　principle,　Euler-Bernoulli　beam　theory　and　piezoelectric　theory.　Runge-Kutta　method　is　introduced　to　simulate　the　nonlinear　output　characteristics　of　the　harvester.　The　results　show　that　the　proposed　model　enables　to　simply　solve　the　parameters,　reduce　calculation　task　and　avoid　the　direct　calculation　of　magnetic　force.　And　the　model　can　describe　the　important　designing　parameters　in　terms　of　the　jump　frequency,　maximum　voltage　and　effective　bandwidth　for　the　mechanism　analysis　of　magnetic　coupled　piezoelectric　energy　harvester.