Electrostatic　pull-in　is　a　famous　instable　behavior　of　an　electrostatic　actuation.　For　most　microbeam　structure　the　beam＇s　highness　and　the　deflection　are　in　same　magnitude　and　thus　should　be　treated　as　a　large　deflection　problem.　A　new　analytical　model　has　been　developed-based　on　energy　method　for　determining　the　pull-in　voltage　of　electrostatically　actuated　fixed-fixed　microbeams.　Effects　of　axial　stress,　residual　stress　and　stretch　stress　gradient　non-linear　stiffening,　and　fringing　fields　are　all　considered.　The　results　have　been　compared　with　published　work　of　other　researchers　and　are　found　to　agree　well　with　the　FEM　results　in　most　common　case.