The invention discloses steel for a pressure bearing boundary part of a steam generator in a nuclear power plant and a manufacturing method of the steel. The steel comprises 0.15% to 0.22% of C, 0.10%to 0.30% of Si, 0.55% to 0.75% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.30% to 0.60% of Ni, 0.70% to 1.10% of Cr, 0.80% to 1.50% of Mo, 0.020% to 0.040% of Al, 0.010% to 0.030% of Nb, 0.0005% to 0.002% of B, less than or equal to 0.05% of Cu and the balance of Fe and unavoidable impurities. A converter-continuous casting process is adopted when the thicknessof a steel plate is less than 80mm, wherein the heating temperature is 1180-1250 DEG C, the rolling starting temperature is greater than or equal to 1100 DEG C, and the rolling finishing temperature is greater than or equal to 900 DEG C; an electric furnace-die casting process is adopted when the thickness of the steel plate is greater than or equal to 80mm, wherein the heating temperature is greater than or equal to 1200 DEG C, the rolling starting temperature is greater than or equal to 1050 DEG C, and the rolling finishing temperature is greater than or equal to 850 DEG C; quenching and tempering treatment are performed on the steel plate after rolling; and the produced steel plate of 30-150mm has good high temperature performance and strong strength-toughness matching.