The　micro-electro-mechanical　system　(MEMS)　resonator　developed　based　on　surface　processing　technology　usually　changes　the　section　shape　either　due　to　excessive　etching　or　insufficient　etching.　In　this　paper,　a　section　parameter　is　proposed　to　describe　the　microbeam　changes　in　the　upper　and　lower　sections.　The　effect　of　section　change　on　the　mechanical　properties　is　studied　analytically　and　verified　through　numerical　and　finite　element　solutions.　A　doubly-clamped　microbeam-based　resonator,　which　is　actuated　by　an　electrode　on　one　side,　is　investigated.　The　higher-order　model　is　derived　without　neglecting　the　effects　of　neutral　plane　stretching　and　electrostatic　nonlinearity.　Further,　the　Galerkin　method　and　Newton-Cotes　method　are　used　to　reduce　the　complexity　and　order　of　the　derived　model.　First　of　all,　the　influence　of　microbeam　shape　and　gap　variation　on　the　static　pull-in　are　studied.　Then,　the　dynamic　analysis　of　the　system　is　investigated.　The　method　of　multiple　scales　(MMS)　is　applied　to　determine　the　response　of　the　system　for　small　amplitude　vibrations.　The　relationship　between　the　microbeam　shape　and　the　frequency　response　is　discussed.　Results　show　that　the　change　of　section　and　gap　distance　can　make　the　vibration　soften,　harden,　and　so　on.　Furthermore,　when　the　amplitude　of　vibration　is　large,　the　frequency　response　softening　effect　is　weakened　by　the　MMS.　If　the　nonlinearity　shows　hardening-type　behavior　at　the　beginning,　with　the　increase　of　the　amplitude,　the　frequency　response　will　shift　from　hardening　to　softening　behavior.　The　large　amplitude　in-well　motions　are　studied　to　investigate　the　transitions　between　hardening　and　softening　behaviors.　Finally,　the　finite　element　analysis　using　COMSOL　software　(COMSOL　Inc.,　Stockholm,　Sweden)　is　carried　out　to　verify　the　theoretical　results,　and　the　two　results　are　very　close　to　each　other　in　the　stable　region.