Abstract: A method of the hidden-line removal is presented which is suitable for the three-dimensional reconstruction on the basis of unparallel two-dimensional section images obtained from sector scanning when the detective head of the ultrasonic is put in the rectum．Several irregular models have been tested by use of the method mentioned above．The results are satisfactory．Finally，the hidden net graph and shade graph observed from the 0angle are given．The research outcome of this paper has laid a firm foundation and has made a necessary preparation of key technologies for clinical practice．