The invention relates to high-strength high dampness and heat sea atmospheric environment resistant weathering resistant steel and a preparing method, and belongs to the technical field of weathering resistant steel. The steel comprises, by weight, 0.01%-0.03% of C, 0.30%-0.50% of Si, 0.60%-0.80% of Mn, 0.90%-1.10% of Cu, 2.80%-3.20% of Ni, 0.20%-0.40% of Mo, 0.25%-0.35% of Sn, 0.05%-0.10% of Sb, not larger than 0.03% of Cr, not larger than 0.02% of Nb, not larger than 0.01% of P, not larger than 0.01% of S, 0.03%-0.05% of RE and the balance Fe. On the basis of a Cu-Ni-Mo alloy system, the Sn, the Sb, the Nb, the RE and other microalloy elements are added, and the Cr content in the weathering resistant steel is greatly reduced. A steel ingot meeting the composition design scope is smelted through a vacuum induction furnace, through the follow-up forging and hot rolling, the weathering resistant steel with the strength of extension larger than or equal to 750 MPa, the yield strength larger than or equal to 650 MPa and the ductility larger than or equal to 15% is finally obtained; the corrosion resistance is reduced by more than 30% compared with a Q450NQR1 traditional weathering resistant steel; and the high-strength high dampness and heat sea atmospheric environment resistant weathering resistant steel is prepared and has the excellent mechanical property.