根据牙轮钻头几何学和运动学原理，分析了钻头齿在井底的运动轨迹和井底轮廓线，提出了确定钻头牙齿与井底接触过程起止点的方法，并运用ＡｕｔｏＣＡＤ绘图软件包建立了确定牙齿与井底接触角的计算机图解法，给出了牙轮钻头设计中的一个应用实例． According to the geometry and kinematics theory of roller cone bit, the movement trajectory and bottom hole contour of bit are analyzed. The method to determine the starting and ending point of bit contact with bottom hole is put forward and the AutoCAD drawing software package is used to establish A computer graphic method of determining the contact angle between tooth and bottom hole gives an example of application in cone bit design.