Steel plate suitable for high heat input welding were industrially produced by employing advanced steel-making technology and thermo-mechanically controlled processing and accelerated cooling technology.A homogenously distributed acicular ferrite microstructure across the thickness direction of the rolled plates was observed,and densely distributed inclusions with a size range from 0.I ~ 3 μm which trigged intra-granular ferrite were revealed.Mechanical properties were measured at quarter and center thickness of the hot rolled steel plate in both transverse and longitudinal direction,which exhibits a yield strength;390 MPa,tensile strength≥510 MPa,elongation≥25%and impact toughness at -60℃≥100 J.Electro-gas welding with a heat input 380 kj/cm was employed to butt weld the 40 mm thick plate,and microstructure and mechanical property of the welded joint were investigated.A narrow coarse grain heat affected zone having a microstructure of 900-/o intra-granular ferrite ( 5 - 15 μm) and 10% grain boundary ferrite (≤5μm in thickness) is found,and its impact toughness at - 20℃≥100 J.The weld joint failed in base metal during tensile test.Satisfactory strength and toughness property of the weld joint implies the good weldability of the plate.