This　article　describes　a　new　magnetorheological　fluid　damper;　its　damping　and　stiffness　are　variable　and　controllable　through　the　compact　structure　of　two　damping　units　and　a　spring.　The　ability　of　variable　stiffness　and　damping　enables　it　to　be　used　for　more　effective　vibration　control　in　wide-band　excitation　wave　occasions.　First,　the　effective　stiffness　and　output　damping　force　are　calculated　in　theory.　Then,　the　magnetic　field　is　simulated　by　finite　element　analysis.　After　the　prototype　of　the　new　magnetorheological　fluid　damper　is　developed　and　machined,　the　damper＇s　performances　are　tested　in　a　hydraulic　actuated　MTS　machine,　including　stiffness　variability　and　damping　variability　in　different　current.　The　successful　development,　numerical　calculation,　and　experimental　testing　shows　that　the　new　damper　not　only　outputs　a　controllable　damping　force　but　also　occurs　as　the　great　variable　stiffness　in　a　certain　range,　which　makes　the　true　design　and　implementation　of　the　concept　of　variable　stiffness　and　damping.