The invention relates to a high-strength ultra-thick steel plate and a production method thereof. The chemical components of the steel plate include, by weight, 0.0025-0.025% of C, 0.16-0.36% of Si, 0.85-1.15% of Mn, 2.1-4.5% of Ni, 0.8-1.2% of Cu, 0.008-0.035% of Ti, 0.8-1.2% of Al and the balance Fe and unavoidable impurities. The high-strength ultra-thick steel plate adopts an ultra-low carbon component, the alloy contents of Ni, Cu, Al and Ti are reasonably configured, a normalizing plus tempering process is adopted, and three nanoscale intermetallic compounds of Ni3Al, Ni3Cu and Ni3Ti and a Cu-rich phase are sufficiently formed in the tempering process. The thickness of the steel plate made from the components and through the process is larger than or equal to 100 mm, the yield strength Rp0.2 is larger than or equal to 900 MPa, the tensile strength Rm is larger than or equal to 1000 MPa, the percentage elongation after fracture is larger than or equal to 12%, the welding performance, cold bending performance and a plate profile are good, the grain performance in the thickness direction is uniform, and a plate thickness effect is avoided. The steel plate produced through the method can be widely applied to various large-thickness steel plate application fields such as heavy engineering machinery, large building structures and bridge structures.