Steel plate and manufacturing method thereof

The invention provides a steel plate and a manufacturing method thereof. The steel plate comprises 0.12-0.18% of C, 0.20-0.45% of Si, 1.30-1.70% of Mn, less than 0.010% of S, less than 0.020% of P, 0.020-0.060% of Nb, 0.010-0.030% of Ti, 0.035-0.070% of V, 0.35-0.70% of Cr, 0.10-0.40% of Ni, 0.20-0.50% of Mo, 0.008-0.0030% of B, 0.020-0.050% of Alt, and the balance of Fe and unavoidable impurities, wherein Alt refers to all aluminum. The steel plate is 100-120mm in thickness, greater than 690MPa in yield strength, greater than 770MPa in tensile strength, greater than 14% in percentage elongation after fracture, and greater than 100J in subzero 20 DEG C longitudinal impact energy.