In this paper, the 390 MPa grade test steel for offshore platform is obtained with the component system of low C, high Mn and Nb-Ti microalloying and reasonable adding sequence of alloys during smelting as well as the controlled rolling and controlled cooling process. The test results showed that the upper yield strength was 488 MPa, tensile strength was 550 MPa, elongation after fracture was 30%, longitudinal and transverse impact energies at -20 ℃ were 242 J and 155 J; the microstructure was fine ferrite and pearlite as well as the inclusions were fine and with the size of 2~3 μm; after the welding thermal simulation test with welding heat input of 100 kJ/cm for test steel, the mechanical property test and metallographic structure were with the basic characteristics of steel with large heat input welding as well as the products are verified to be with good low-temperature impact toughness and welding performances.