In　nanomechanical　QED　system,　consisting　of　a　charge　qubit　and　a　nanomechanical　resonator　with　intrinsic　nonlinearity,　we　study　the　temporal　behavior　of　Rabi　oscillation　in　the　nonlinear　Jaynes　Cummings　model.　Using　microscopic　master　equation　approach,　we　solve　time　evolution　of　the　density　operator　describing　this　model.　Also,　the　probability　of　excited　state　of　charge　qubit　is　calculated.　These　analytic　calculations　show　how　nonlinearity　parameter　and　decay　rates　of　two　different　excited　states　of　the　qubit-resonator　system　affect　time-oscillating　and　decaying　of　Rabi　oscillation.