Abstract: It is a large amount of welding in the ring seam of nuclear steel containment cylinder, and the welding efficiency and welding quality can be effectively improved by using the submerged arc transverse welding process.In this paper, the submerged arc horizontal welding process of SA-738Gr. B plate with 42mm thickness was studied.The results show that compared with K-type groove, it was easier to avoid porosity and slag inclusion defects by using X-type groove for bottom welding. The submerged arc horizontal welding process was tested with different heat input parameters. When the heat input is too small, the weld was poorly formed and easy to produce unfused defects. The impact toughness test and hardness test of welded joints under different heat input were carried out, and the test results meet the standard requirements. Through this study, it was proved that the submerged arc welding of steel containment is reliable and the welding joint performance meets the standard requirements, which provides some guidance for the popularization and application of the new technology in nuclear power field.