In this paper,the variation of blood flow velocity wave along the radial position of carotid artery is analyzed,and the influence of the radial position on velocity maximum(Vmax)and minimum(Vmin)are discussed in detail.These results are applicable for assessing the effect of the ultrasonic probe deviating from the axis of carotid artery on the measured Velocity measurement can be controlled to around 10 percent when the probe deviated its position from the blood vessel axis is y=r/R=0.2.This plays an important role in the operation and analysis of non-invasive blood flow velocity measurement.