The invention provides a preparation method for a high-
toughness 3.5Ni steel plate in order to reduce the production cost and belongs to the field of
alloy steel manufacture. The preparation method comprises the steps that (1) hot rolling is conducted, a
casting blank is put into a
heating furnace with the temperature of 1150 DEG C-1200 DEG C for heat preservation for 1-2 h, the
casting blank comprises, by weight, 0.04%-0.07% of C, 0.10%-0.25% of Si, 0.60%-0.90% of Mn, 0-0.005% of S, 0-0.008% of P, 0 or 3.3%-3.8% of Ni, 0-0.60% of Cr, 0-0.04% of Mo, 0.02%-0.05% of Alt and the balance Fe and impurities; two-stage rolling is adopted for hot rolling, and the total
compression ratio of the steel plate is the thickness of the
casting blank / the thickness of a finished product>=5.00; and (2) direct hot rolling is conducted, the rolled steel plate is quenched directly or after the relaxation for 10-20 s to below 300 DEG C through
ultra fast cooling at the speed of larger than or equal to 20 DEG C / s, then the plate is put into a
heating furnace with the temperature of 570 DEG C-620 DEG C for heat preservation, after that, the product is obtained after the steel plate is cooled through water or air to the
room temperature. According to the preparation method, direct
quenching and
tempering processes are adopted, so that the process flow of hot treatment is shortened, and the cost is lowered; in addition, the
austenite grain size is refined by controlling the rolling process, and the low-temperature
toughness and other mechanical properties of 3.5Ni steel are significantly improved.