Extra-thick-gauge Q690 high-strength Structural steel plate and preparation method of structural steel plate

The invention relates to an extra-thick-gauge Q690 high-strength structural steel plate. The thickness of the steel plate is 160-180mm; the steel plate takes Fe as a basic element and comprises the following components in percentage by mass; 0.15%-0.18% of C, 0.15%-0.35% of Si, 1.00-1.20% of Mn, no more than 0.015% of P, no more than 0.005% of S, 1.00%-1.20% of Cr, 0.54%-0.60% of Mo, 0.80%-1.00% of Ni, no more than 0.30% of Cu, 0.02%-0.04% of Al, 0.03%-0.05% of V, 0.02%-0.04% of Nb, 0.01%-0.02% of Ti, no more than 0.005% of N, 0.001%-0.002% of B, and inevitable impurity elements; the equivalent carbon content is smaller than or equal to 0.78. The preparation process of the steel plate comprises the following steps: smelting blanks; heating the blanks; descaling by high-pressure water; rolling; straightening; DQ-ACC online quenching; slow cooling; and tempering; the maximal thickness of the prepared steel plate can reach 180mm; the structural steel plate has relatively high hardenability; and various mechanical properties reach the industry level.