Guide joint bearing is the transmission mechanism of torque and bit weight in the controllable bend joint of rotary guide drilling tool.The clearance between steel ball and channel in the guide joint bearing will affect the accuracy and stability of the bias angle of the guide shaft in the controllable bend sub.According to the structural characteristics of steel ball and channel,the geometric model of steel ball and channel section,the surface equation and mathematical model of channel surface were established.According to the geometric model of steel ball and channel section,the circumferential clearance between the steel ball in spherical shell and the steel ball in spherical sleeve and the channel in guide joint bearing was calculated by MATLAB.The results show that the spherical channel surfaces inside and outside the guide frame are elliptic surface.No matter which direction the guide axis is offset,it has no influence on the circumferential clearance angle of the steel ball.When the bias angle of the guide shaft is zero,the total circumferential clearance angle of the steel ball is constant and maximum,when the bias angle is not zero,the circumferential clearance angle changes periodically and presents a fluctuation with the increase of the bias angle.The fluctuation of the circumferential clearance angle between the steel ball in the sleeve and the channel is greater than that between the steel ball in the spherical shell and the channel,which is an important reason for the vibration and noise of the guide shaft during rotation.