In　order　to　study　the　damping　mechanism　of　non-packed　particle　damper　(NPPD)　in　depth,　the　analysis　of　energy　variation　and　the　damping　mechanism　of　physical　parameters　are　carried　out　successively　based　on　the　proposed　double　inertia　mass　equivalent　model　(DIMEM).　Firstly,　the　DIMEM　is　described　briefly　with　emphasis　on　the　establishment　of　DIMEM,　the　differential　equations　of　motion　of　DIMEM-SDOF　structure　and　the　experimental　verification　of　model.　Then,　the　periodic　energy　consumption　index　and　the　periodic　momentum　exchange　index　are　defined.　The　damping　mechanisms　of　different　physical　parameters　are　discussed　based　on　the　proposed　index.　Finally,　the　analyses　of　damping　performance　of　NPPD　under　free　vibration,　resonant　harmonic　excitation　and　earthquake　are　carried　out　based　on　the　DIMEM.　The　energy　change　rule　and　proportion　in　vibration　control　are　discussed.　The　results　show　that　the　energy　of　the　system　is　mainly　dissipated　by　the　interaction　between　particles.　The　damping　performance　of　NPPD　is　affected　comprehensively　by　energy　consumption　and　momentum　exchange.　It　is　difficult　to　explain　the　variation　law　of　damping　effect　only　by　analyzing　the　energy　consumption.　The　vibration　reduction　effect　and　mechanism　analysis　of　NPPD　based　on　DIMEM　is　of　great　significance　for　further　understanding　of　particle　damper　and　parameter　optimization.　©　2022,　Editorial　Office　of　China　Civil　Engineering　Journal.　All　right　reserved.