The invention belongs to the technical field of metallurgy and particularly relates to copper-containing low-carbon high-strength high-ductility steel for an ocean platform and a preparation method thereof. The copper-containing low-carbon high-strength high-ductility steel for oceanographic engineering consists of the following chemical components in percentage by weight: 0.06-0.11% of C, 0.15-0.35% of Si, 0.95-1.3% of Mn, 0.4-0.6% of Mo, 2.3-2.8% of Ni, 0.5-1.0% of Cr, 1.0-2.0% of Cu, less than and equal to 0.05% of Nb, less than and equal to 0.08% of V, greater than and equal to 0.02% of Al, less than and equal to 0.025% of P, less than and equal to 0.010% of S and the balance of Fe, wherein yield strength is 785-820 MPa, tensile strength is 870-925 MPa, and low-temperature impact powerat (-)40 DEG C is 140-220 MPa. The preparation method comprises the following steps of: roughly milling and finely milling forged steel billets in an austenite re-crystallization region and an austenite a non-recrystallization region to obtain a hot-rolled steel plate; and performing QLT two-step critical thermal treatment on air-cooled steel, wherein a quenching temperature is 850 DEG C, a critical annealing temperature is 680 DEG C, a critical tempering temperature is 620 DEG C and heat-preservation time is 60 minutes. The copper-containing low-carbon high-strength high-ductility steel is reasonable in component design, and is simple and easy in process control; and the obtained steel has ultrahigh strength and good low-temperature toughness.