The invention discloses a DIWA373 steel plate for a super-thick high-pressure boiler and a production method thereof. The steel plate comprises the following chemical components by mass: less than orequal to 0.17% of C, 0.25%-0.50% of Si, 0.80%-1.20% of Mn, less than or equal to 0.010% of P, less than or equal to 0.008% of S, less than or equal to 0.30% of Cr, 1.00%-1.30% of Ni, 0.25%-0.50 % of Mo, 0.50% to 0.80% of Cu, 0.015% to 0.045% of Nb, greater than or equal to 0.015% of Alt, and balance of Fe and unavoidable impurities. The steel plate has the effect of fine grain strengthening and precipitation strengthening by adding of alloying elements such as Ni, Cu, Mo and Nb, the high temperature strength and the permanent strength of the steel can be improved; and by strict controlling ofthe content of harmful elements P and S, gases and inclusions in a pipe, the horizontal low temperature toughness index can be ensured. The steel plate has good comprehensive mechanical properties andhigh stability. The method achieves good toughness matching through reasonable component design and heat treatment process, and meets good high temperature creep resistance and low yield ratio, and the ultrasonic flaw detection of the steel plate also meets the requirements of NB/T47013-2015.