This　work　aims　to　identify　ways　to　achieve　dynamic　performances　of　a　novel　double-layer　vibration　isolation　system　(DL-VIS)　capable　of　achieving　multi-directional　isolation　and　extreme　environmental　adaptability.　A　forward　modeling　approach　applicable　to　complex　systems　has　been　developed　and　analyses　of　nonlinear　dynamic　characteristics　under　different　working　conditions　are　performed.　First,　by　integrating　with　constitutive　models　in　terms　of　individual　elastic　elements　and　the　connective　relationships　within　the　structure,　multidirectional　constitutive　models　for　isolation　devices　are　established.　Further,　the　decomposition　of　linear　and　nonlinear　stiffness　components　in　different　directions　is　performed　using　the　Taylor　expansion　method.　Subsequently,　the　dynamic　response　under　sinusoidal　sweep　frequency　loading　is　obtained　using　the　related　stiffnesses　in　the　dynamic　model　and　adopting　the　extended　harmonic　balance　method.　The　effects　of　stiffness,　damping,　and　a　nonlinear　stiffness　gradient　on　the　DL-VIS　response　are　thoroughly　evaluated.　Finally,　the　vibration　isolation　performance　and　nonlinear　dynamics　under　different　working　conditions　are　examined,　and　the　proposed　dynamic　model　is　experimentally　validated.　The　results　indicate　that　the　response　of　DL-VIS　varies　significantly　under　different　working　conditions,　particularly　under　overload　conditions.　The　nonlinear　characteristics　lead　to　wide-band　instability　near　the　natural　frequency　and　excellent　vibration　attenuation　performance　in　multiple　directions.　The　theoretical　model　agrees　well　with　the　experimental　results　in　the　nonresonant　region　and　near　the　first　resonant　peak,　which　proves　the　prediction　accuracy　in　the　low-frequency　range.　These　findings　provide　robust　theoretical　and　technical　support　for　the　design　and　performance　optimization　of　isolation　systems.　©　2024　The　Author(s).　International　Journal　of　Mechanical　System　Dynamics　published　by　John　Wiley　&　Sons　Australia,　Ltd　on　behalf　of　Nanjing　University　of　Science　and　Technology.