To promote the mechanical properties of marine high strength steels joints, fiber laser butt welding on 8 mm thick 10CrSiNiCu steel is performed by using filler wire. The microstructures, hardness, tensile strength, bending property and impact energy (at sub-zero temperature) of the welded joints are analyzed. Also, the effects of welding heat input on microstructures, hardness and fracture behavior of the welded joints are also studied. The results show that the microstructure of the weldment mainly consists of martensite + ferrite + bainite, and its hardness is the highest among the welded joint zones. When heat input decreases from 5.00 kJ/cm to 3.64 kJ/cm, the average hardness of weldment increases from 346 HV to 396 HV. Tensile specimens are all broken in base metal. A bending angle of 113° can be reached at room temperature, which is 60° lower than base metal. At the heat input of E=4.20 kJ/cm, the impact energy at fusion line and weld seam reaches its highest value, 95 J and 101 J, respectively.