A　new　type　of　velocity　adjustable　tuned　mass　damper　(TMD)　consisting　of　impulse　generators　and　clutches　is　presented.　The　force　impulse　is　generated　by　a　joining　operation　of　electromagnets　and　springs　and　MR　dampers　are　used　as　clutches.　Rules　for　velocity　adjustment　are　established　according　to　the　working　mechanism　of　TMD.　The　analysis　program　is　developed　on　a　VB　platform.　Seismic　response　of　SDOF　structures　with　both　passive　TMD　and　velocity　adjustable　TMD　are　analyzed.　The　results　show　that　(1)　the　control　effectiveness　of　passive　TMDs　is　usually　unstable;　(2)　the　control　effectiveness　of　the　proposed　semi-active　TMDs　is　much　better　than　passive　TMDs　under　typical　seismic　ground　motions;　and　(3)　unlike　the　passive　TMD　system,　the　proposed　velocity　adjustable　TMDs　exhibit　good　control　effectiveness　even　when　the　primary　structure　performance　becomes　inelastic　during　severe　earthquakes.