本发明公开了一种大线能量焊接用海洋工程用钢及其制备方法，其化学成分的质量百分含量为：C 0.04%～0.11%，Si 0.13%～0.22%，Mn 1.1%～2.1%，P≤0.012%,S≤0.015%,Nb 0.008%～0.02%，N 0.003%～0.008%，Al 0.002%～0.008%，Zr 0.001%～0.008%，Ti 0.008%～0.024%，Ca 0.0005%～0.004%，余量为Fe及其他不可避免杂质元素；所述钢中（Ca,Al,Ti,Zr）Ox‑MnS夹杂物尺寸为0.31～2.7μm，面密度为695～1404个/mm；所述钢的焊接热影响区组织中针状铁素体含量高于60%。本钢中（Ca,Al,Ti,Zr）Ox‑MnS夹杂物可以起到钉扎奥氏体晶界和促进针状铁素体形成的作用；钢板焊接热影响区组织中针状铁素体的形成能细化焊接热影响区晶粒，微裂纹解理跨越针状铁素体时会发生偏转，裂纹扩展需要更高的能量，钢板钢焊接热影响区表现出良好的低温冲击韧性。

The invention discloses a marine engineering steel for large energy input welding and a preparation method thereof. The marine engineering steel comprises chemical components, in mass percent, 0.04% to 0.11% of C, 0.13% to 0.22% of Si, 1.1% to 2.1% of Mn, <=0.012% of P, <=0.015% of S, 0.008% to 0.02% of Nb, 0.003% to 0.008% of N, 0.002% to 0.008% of Al, 0.001% to 0.008% of Zr, 0.008% to 0.024% ofTi, 0.0005% to 0.004% of Ca, and the balance of Fe and other unavoidable impurity elements. In the steel, the (Ca, Al, Ti, Zr)Ox-MnS inclusion has size of 0.31 to 2.7 [mu]m, and an areal density of 695 to 1404 / mm2. The acicular ferrite content in a welding heat affected zone of the steel is higher than 60%. The (Ca, Al, Ti, Zr)Ox-MnS inclusion has an effect of pinning the austenite grain boundaries and promoting the formation of the acicular ferrite. The formation of the acicular ferrite in the welding heat affected zone of the steel can refine the grains in the welding heat affected zone. Microcrack cleavage can be deflected when stepping over the acicular ferrite. The crack propagation requires higher energy. The welding heat affected zone of the steel shows good low-temperature impact toughness.