Abstract: In view of the problems of poor flexibility, low degree of automation, and insufficient stability of joint quality of the current saddle-shaped weld welding equipment, a new type of external anchored four-axis welding robot was developed. The D-H link coordinate system is established by rationally simplifying the robot mechanism, the forward and inverse kinematics expressions of the robot are deduced, and the uniqueness of the inverse kinematics solution is determined by combining the limit values of the robot joint variables. The kinematics of the robot is simulated by MATLAB software, and the simulation results show that the derived forward and inverse kinematic equations are completely correct. Welding experiment by making a prototype, the experimental results show that the welding seam is compact and beautiful, and the deviation of the robot welding torch trajectory in the x, y and z directions is within ±0.35 mm, which fully meets the needs of automatic welding in engineering. It provides the theoretical basis and algorithm support for the continuous trajectory control and offline programming of the saddle-shaped seam welding robot.