The invention discloses a quenching and tempering heat treatment production method of a nuclear power I-grade safety cover ultra-thick steel plate. The quenching and tempering heat treatment production method adopts a quenching process and a tempering process; the quenching temperature is 900-930 DEG C, the total heating time is 140-260 min, the maximum water volume is larger than or equal to 7600m^3, and the roll speed is 2.0-2.2 m/min; and the tempering temperature is 640-680 DEG C, the total heating time is larger than or equal to 4.5 min/mm, and discharging and air cooling are performed.According to a tempered bainite and ferrite structure with refined grains obtained through the method, the grain size of the structure is 7.5-8.5 grades, the yield strength is larger than or equal to650 MPa, the tensile strength is 700-860 MPa, A50 is larger than or equal to 18%, the anti-lamellar tearing performance value is larger than or equal to 55%, the minus 18 DEG C low-temperature impacttoughness average value is larger than or equal to 120J, the lateral expansion amount is larger than or equal to 0.85 mm, the method is simple, the product quality is stable, and the batch productioncan be realized.