Abstract: The tool coordinate system was calibrated according to six-point calibration method. First,it calibrated the position vector of the tool parameters,followed by calibration of orientation matrix of the tool coordinate system,which used the matrix form of the linear least squares to fit tool center point position and the basic operations of the vector and the matrix transformation to calculate tool coordinate frame orientation. For the RB_1400 six-DOF welding robot,the paper developed the tool coordinate system calibration algorithm module and the welding gun pose transformation module based on the automation software CODESYS. Finally,by executing a movement to the reference point,which uses the result data of the developed function block,the test checked whether TCP can meet the requirements when moving around the x,y,and z axis separately. Result shows that the method is feasible and can be also applied to other types of calibration of the robot tool coordinate system.