Microcirculations　are　classified　by　capillary　diameter　and　speed　of　blood　flow.　Each　kind　of　microcirculation　has　its　corresponding　method　to　measure　velocity.　Fast　Fourier　Transform　(FFT),　a　kind　of　signal　processing　methods,　was　introduced　in　this　paper.　The　methods　for　blood　average　velocity　measurement　were　analyzed　systematically.　The　conventional　methods　was　improved　by　introducing　new　method　(FFT)　into　the　measurment.　Results　show　that　the　measurement　become　simple　after　being　classified,　the　real　time　performance　and　veracity　were　improved.　Many　good　results　have　been　obtained　from　FFT.