in this paper , the input impedance of a pulsative flow through a vessel with mild stenosis amplitude radically was investigated .The calculate of arteria femoralis of dog showed no matter which kind of stenosis parameters change ,the input impedance of the zero order harmonic frequency is the largest ,and the others reduce successively .There is a fluctuation when it comes to the second order harmonic frequency ,which accords with the physiology fact. The frequency of the stenosis amplitude oscillatory makes the input impedance periodically change in a cardiac cycle. But the character of the wall of the tube has little effect on the input impedance.