To　study　the　characteristics　and　the　generation　mechanism　of　the　secondary　vibration,　a　theoretical　model　is　built　up　and　the　dynamic　equations　are　derived.　Analysis　results　show　that　the　structural　secondary　vibration　is　a　resonance　vibration　of　some　components　such　as　beams　and　floors,　under　the　traffic-induced　vibration　excitation　with　a　close　dominant　frequency　to　the　components.　Based　on　a　real　project,　a　7-story　frame　structure,　the　internal　secondary　vibration　reoccurred　under　different　traffic　vibrations　excitated　by　elevated　road,　subway,　and　light　railway,　respectively,　which　validated　the　feasibility　of　the　proposed　theoretical　model　and　the　derivation　of　structural　secondary　vibration　in　this　paper.