In order to realize the assembly and welding of large arched box steel structures,a tooling was developed,which was used for submerged arc welding,and the welding process and welding deformation were studied. The results show that when the welding gun inclination angle θ is in the range of 7°～10°,the incomplete penetration at the root of the weld can be reduced. In addition,the two welds on one side of the box structure are welded simultaneously in the same direction,inverted after welding,and then welded simultaneously in the same direction to the two welds on the other side,and the welds on the upper and lower sides are measured by measurement. The shrinkage occurs simultaneously in the lateral direction,the shrinkage amount is 2 ～4 mm,and there is almost no change in the vertical direction,and the difference between the two diagonal dimensions is not more than 2 mm. In summary,under the above-mentioned tooling and process welding,the welding deformation is controlled to meet the engineering requirements.