The　main　target　of　monetary　policy　in　China　is　the　money　supply,　and　according　to　the　quantity　theory　of　money,　the　national　income,　price　level　and　the　monetary　velocity　must　be　studied　in　order　to　set　up　the　goal　for　money　supply,　which　is　harder　to　measure　because　it＇s　affected　by　many　other　interactive　variables.　In　this　paper,　the　monetary　velocity,　growth　rate　of　money　supply　in　the　short　time　and　especially　its　trend　after　the　subprime　crisis　is　analyzed　firstly,　then　the　model　of　monetary　velocity　is　set　up　in　a　longer　time　from　1990　to　2009,　showing　that　monetary　velocity　is　going　down　in　the　long　time.　Finally,　this　trend　and　its　reason　are　revealed.　©　2011　IEEE.