This　study　presents　some　novel　results　about　analysis　and　design　of　low-frequency　or　broadband-frequency　vibration　isolation　using　a　hybrid　lever-type　isolation　system　with　an　X-shape　supporting　structure　in　passive　or　semi-active　control　manners.　It　is　shown　that　the　system　has　inherent　nonlinear　stiffness　and　damping　properties　due　to　structure　geometrical　nonlinearity.　Theoretical　analysis　reveals　that　the　hybrid　isolation　system　can　achieve　very　good　ultra-low-frequency　isolation　through　a　significantly-improved　anti-resonance　frequency　band　(by　designing　structure　parameters).　Noticeably,　the　system　can　realize　a　uniformly-low　broadband　vibration　transmissibility,　which　has　never　been　reported　before.　Cases　studies　show　that　the　system　can　work　very　well　with　good　isolation　performance　subject　to　multi-tone　and　random　excitations.　The　results　provide　a　new　innovative　approach　to　passive　or　semi-active　vibration　control　(e.g.,　via　a　simple　linear　stiffness　control)　for　many　engineering　problems　with　better　ultra-low/broadband-frequency　vibration　suppression.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.