Abstract: According to GB/T2358-1994 standard,the crack tip opening displacement(CTOD) of 16mm thick steel 10Ni3CrMoV center seam of welded joints the crack tip opening displacement(CTOD) at temperature-40 ℃ was tested.The majority of the specimen fracture toughness values are satisfactory,with CTOD value over 0.15mm in line with the DNV standard of acceptance.The experimental results show that with given two-wire submerged arc welding process,the low temperature toughness of the steel welds is good and the joint of medium thickness steel plant with twin-wire submerged arc welded technics can be used without heat treatment after welding.