The invention discloses an ocean platform steel plate with a thickness of 80-120 mm and a production method thereof. The ocean platform steel plate comprises the following chemical components in percentage by mass: 0.08-0.12 of C, 0.17-0.30 of Si, 1.2-1.3 of Mn, 0.08-0.012 of P, 0.3-0.5 of Cu, S not more than 0.005, 3.5-4.5 of Cr+Mo+Ni, V+Nb+Ti not more than 0.1, B not more than 0.001, 0.25-0.50 of Als, and the balance of Fe and residual elements. The production method comprises the steps of: pretreatment of high-quality molten iron and KR molten iron, 100/120 t basic oxygen steel making converter, LF furnace refining, vacuum degassing treatment, steel ingot stack cooling, steel push heating furnace, 3800 m rolling mill, ACC laminar cooling, 11 roller heat straightener, stack cooling, finishing, performance inspection, external inspection, flaw detection and warehousing. Through reasonable chemical component design, the LF+VD process guarantees the steel cleanness; and through effective actuation of such processes as heating, rolling, cold control and stack cooling, the yield strength is controlled within 690-720 MPa, the tensile strength is controlled within 790-830 MPa, the elongation is controlled with 21-23%, and the V type impact power is controlled within 80-110 J.