Abstract: Aiming at the robot welding of a large valve annular weld, the influence of process parameters on the forming quality of single pass weld was studied firstly, and the process model between the weld straightness and welding current, welding torch angle and welding speed was established. Based on the model, the optimal process parameters were predicted. Finally, the optimal parameter combination was applied to the multi-layer and multi-channel welding of a large valve annular weld. The results show that the influence degree of each process parameter on the weld flatness is as follows:welding torch angle > welding current≈welding speed; the process parameters corresponding to the best weld forming quality are welding current of 144 A, welding speed of 1.6 mm/s and welding torch angle of 88°. The welding of the large butterfly valve was realized by using the process parameters, and the surface of the welded joint is flat without cracks and unmelted defects. The weld microstructure is pearlite and ferrite, and the grains are fine and uniform. The tensile strength of the joint is 536 MPa, the yield strength is 468 MPa, the elongation is 14%, and the impact absorbing energy is 36 J at 0 ℃, which can meet the use demands.