Abstract: The S355ML steel used in extremely cold areas has the characteristics of high strength and strict requirements for low-temperature toughness. By reasonably selecting welding materials and controlling the preheating temperature, maximum interlayer temperature and heat input, a submerged arc welding process of S355ML steel is developed for extremely cold areas with low temperature toughness of-50℃. The results of the welding process qualification test of submerged arc welding show that the strength of the joint meets the requirements, the plasticity is good, and the low-temperature toughness far exceeds the qualified value of the project.The process development is successful.