Abstract: The welding technology of complex thin-walled parts was studied using the combination of the technology of additive manufacturing and arc welding robot. Firstly, on the basis of the traditional stratification method the geometric model of high variation in the forming process is predicted and analyzed. And then through the robot's off-line programming and trajectory planning technology, the automatic extraction of the forming trajectory is realized. The circular discrete local approximation algorithm is used to differentiate the serial sections of complex thin-walled parts, and the quaternion matrix is calculated to achieve the automatic adjustment of welding torch position and pose. And the welding process is improved to ensure the forming quality. Finally, some thin walled parts were welded for experimental verification. The results show that the forming of thin-walled parts is of good quality, and the error between the predicted size and the actual forming size is not more than 1 mm.