Abstract: In order to improve the qualification rate of ultrasonic testing for continuous casting extra thick slab, reduce the production cost of heavy plates, and prevent quality defects such as "white spots", "hydrogen embrittlement", and "point segregation", and overcome the difficulties of traditional experimental methods for detecting hydrogen diffusion in extra thick slab, a numerical simulation method was used to study the process of reducing hydrogen concentration in steel to a safe range through stacking cooling, and good results were achieved. Due to the thickness of the continuous casting slab reaching 400 mm, it takes a long time for hydrogen to diffuse from its core to the surface. Ordinary stacking slow cooling cannot meet the hydrogen removal effect of the slab. Therefore, using slow cooling pits and slow cooling pit heating methods for stacking slow cooling can further improve the insulation effect of the slab and make the hydrogen diffusion of the slab more sufficient. Therefore, a mathematical model for hydrogen diffusion in slab was established based on three stacking methods. The effects of ordinary stacking, slow cooling pit stacking, and slow cooling pit heating on hydrogen diffusion in slab were compared, and the hydrogen content and hydrogen removal rate at each position of the slab were obtained. Under the three stacking modes of ordinary stacking, slow cooling pit stacking, and slow cooling pit heating, the hydrogen removal rates of the bottom slab were 58.93%, 67.63%, and 71.98%, respectively. The slow cooling pit stacking method and slow cooling pit heating method are not only more conducive to the hydrogen diffusion in extra thick slab but also can make the hydrogen diffusion on the upper and lower surfaces of the extra thick slab more uniform.