To　promote　the　application　of　non-stacked　particle　damper　(NSPD)　in　civil　engineering,　a　design　methodology　was　suggested　on　the　basis　of　the　double　inert　mass　equivalent　model.　NSPD　single-story　steel　frame　model　is　selected　as　the　research　object　in　this　paper.　First,　the　analytical　solution　for　the　periodic　motion　with　symmetric　two　impacts　was　discussed.　The　shaking　table　test　was　performed　to　verify　the　rationality　of　the　analytical　solution　under　harmonic　excitation.　Subsequently,　based　on　the　analytical　solution,　the　influence　of　equivalent　connection　stiffness　on　the　vibration　reduction　effect　and　mechanism　was　analysed　under　resonant　and　non-resonant　harmonic　excitation.　The　numerical　analysis　methods　of　the　optimal　equivalent　connection　stiffness　were　obtained　accordingly.　Finally,　the　effectiveness　and　generalization　of　the　proposed　optimal　equivalent　connection　stiffness　were　discussed　numerically　under　harmonic　excitation　and　seismic　ground　motion.　An　optimal　design　process　for　the　NSPD　was　proposed　accordingly.　Based　on　this,　the　vibration　reduction　performance　analysis　of　NSPD　under　far-field　records,　near-fault　pulse-like　records　and　near-fault　non-pulse　records　was　further　conducted　in　the　end.　The　results　show　that　the　time-dependent　frequency　behaviour　of　the　uncontrolled　structure　has　a　significant　impact　on　the　performance　of　the　NSPD.　The　proposed　optimization　method　is　effective,　which　can　be　used　as　the　foundation　for　the　optimization　of　NSPD　under　earthquakes.