Abstract: The submerged arc welding was carried out on different thickness Q500ME steel plate with KGF-70FD welding wire and KGF-102G flux. For the 20 mm-thickness steel plate, the V-shaped groove was machined, two-layer three-pass welding was carried out on the front side and single-layer single-pass was on the back side. For the 40 mm-thickness sted plate, the X-shaped groove was prepared, four-layer seven-pass welding was carried out on the first side, and two-layer two-pass was on the back side. The microstructure and mechanical properties of the submerged arc weld joints were studied. The results show that the microstructure of the weld with different steel plate thicknesses was mainly composed of proeutectoid ferrite,acicular ferrite and granular bainite, and there was also carbide-free bainite in the weld with 40 mm steel plate thickness. The tensile strength of the full-thickness (20, 40 mm) tensile specimens of the joints was 666 MPa and 692.5 MPa, respectively, which were higher than that of the base metal. The joints did not crack after 180° bending. Compared with those under the steel plate thickness of 20 mm, the impact absorption energy at −40 ℃ of the weld center with the steel plate thickness of 40 mm was greater, and the impact absorption energy in the heat affected zone was smaller. The fracture form of the impact fracture of the joints was the mixture of ductile fracture and cleavage fracture.