Abstract: Using physical simulation method, influence of beneficial inclusions on microstructure was studied in coarse grain welding heat affected zone (CGHAZ)of the oxides metallurgy steel. The inclusions which induced nucleation of acicular ferrite were observed by transmission electron microscope and the chemical composition was also analyzed by energy dispersive X-ray spectroscopy. Results indicated that the beneficial inclusions in CGHAZ of the prepared steel are oxide complexes composed of MnO, TiO_x, SiO₂ and Al₂O₃ or oxide-sulfide complexes composed of such oxides and MnS, CuS or (Mn, Cu)S, and their diameter is 0.2 -0.6 μm.During welding process, beneficial inclusions can induce multidimensional nucleation of acicular ferrite and sympathetic nucleation as well, which make the acicular ferrite in CGHAZ interlocked and grains refined apparently.The microstructure in CGHAZ of the prepared steel has the ability of self-refining.