We　generalize　a　microscopic　master　equation　method　to　study　the　dissipation　dynamics　of　Jaynes-Cummings　two-level　system　with　a　weak　external　driving.　Using　perturbative　analysis　to　extend　the　damping　bases　theory,　we　derive　the　corrected　Rabi　oscillation　and　vacuum　Rabi　splitting　analytically.　The　evolution　of　the　decoherence　factor　of　the　weakly　driven　system　reveals　that　the　off-diagonal　density　matrix　elements　are　oscillating　at　a　frequency　dependent　on　the　driving　strength　and　the　initial　population　inversion.　For　highly　inverted　systems　at　the　weak-driving　limit,　this　frequency　reduces　to　twice　the　value　for　the　non-driven　system,　showing　the　dissipation　dynamics　unable　to　be　discovered　using　more　conventional　approaches.