A method of establishing the motion trajectory model of flexible puncture needle based on image processing is proposed to accurately measure the motion track of the flexible needle during needle insertion.The dynamic images of needle insertion are collected through the camera system,and the position coordinates of the flexible needle tip during needle insertion are extracted using the image processing morphology technology.Based on the extracted needle tip data,the least square method is employed for curve fitting,and the second-order polynomial model,exponential function model,and bicycle model are established.The analysis on the goodness of fit,residual,and residual sum of squares of different models reveals that the second-order polynomial model is superior to the other two models in exploring the optimal solution of the trajectory model of flexible puncture needle.