Abstract: The present invention discloses a seawater-corrosion-resistant steel, the mass percentage of the chemical elements thereof being: 0.03-0.05% of C, 0.04-0.08% of Si, 0.8-1.2% of Mn, 0.1-0.2% of Cu, 2.5-5.5% of Cr, 0.05-0.15% of Ni, 0.15-0.35% of Mo, 1.5-3.5% of Al, 0.01-0.02% of Ti, 0.0015-0.003% of Ca, and the balance being Fe and other inevitable impurities. The present invention further discloses a method for manufacturing the seawater-corrosion-resistant steel. The method includes the following steps: (1) smelting and casting; (2) reheating: reheating a casting blank to 1200° C.-1260° C.; (3) rough rolling; (4) finish rolling; (5) coiling; and (6) cooling to room temperature. The seawater-corrosion-resistant steel has good seawater corrosion resistance and excellent mechanical properties.