Compared　to　the　two-stage　linear　vibration　isolator　(TLVI),　the　two-stage　quasi-zero　stiffness　(TQZS)　system　offers　superior　vibration　isolation　performance,　making　it　a　promising　candidate　for　vibration　isolation　of　precision　instrument.　However,　the　TQZS　system　exhibits　a　significant　vibration　amplitude　due　to　its　low　dynamic　stiffness.　In　this　paper,　a　coupled　(TQZS-UDVA)　system　consisting　of　a　TQZS　system　and　a　dynamic　vibration　absorber　(DVA)　attached　to　the　upper　stage　of　the　TQZS　system　is　presented.　The　harmonic　balance　method　is　employed　to　obtain　approximate　analytical　solution.　The　effects　of　system　parameters　on　dynamic　behavior　and　isolation　performance　are　studied　in　detail.　Five　performance　indexes　are　proposed,　and　based　on　these　indexes,　the　damping　and　tuning　stiffness　of　DVA　are　optimized.　The　results　indicate　that　the　integration　of　DVA　effectively　mitigates　the　vibration　amplitude　and　extends　the　isolation　frequency　band,　without　compromising　high-frequency　performance.