Abstract: Objective The aim is to obtain welded joints with excellent comprehensive properties such as strength and toughness through reasonable design of DH36 and EH420 steel welding processes, which is of great significance for the construction of deep-water jacket. Methods Domestic DH36 and EH420 steels are selected as the research object, and their welding processes are developed through the combination of flux-cored arc welding and submerged arc welding processes, and the welded joints are tested by nondestructive testing as well as physical and chemical properties testing. Results The reduced section tensile strength of the welded joint is ≥570 MPa, the hardness is ≤225 HV, and the impact absorbed energy of the weld center is ≥138 J. The impact performance on the EH420 side is significantly better than that on the DH36 side. The minimum impact absorbed energy on EH420 side is 189 J , and the maximum impact absorbed energy is ≥300 J. The minimum impact absorbed energy on DH36 side is 70 J , and the maximum impact absorbed energy is 232 J. The fracture toughness of the weld center and EH420 side at −10 ℃ is good, and the CTOD is ≥0.3 mm. The fracture toughness on DH36 side decreased significantly at −10 ℃ due to the existence of banded structure, but it still maintain good fracture toughness at 0 ℃, and the CTOD is ≥0.98 mm. Conclusion The welded joint of DH36/EH420 steel has good room temperature tensile properties, low temperature impact toughness and fracture toughness, which meets the requirements of a 300 m water depth jacket design standard in the South China Sea.