The invention discloses a dehydrogenization annealing method for electroslag type hydrochrome molybdenum steel. The method comprises heating, heat preservation and cooling processes. In the heating process, steel plate charging temperature is 300 to 400 DEG C; after a steel plate is placed into a furnace, steel braising is performed at furnace temperature of 300 to 400 DEG C, and then the temperature rises up to heat preservation temperature. In the heat preservation process, the heat preservation temperature is 610 to 630 DEG C. In the cooling process, after being subjected to heat preservation, the steel plate is cooled in the furnace to 200 to 300 DEG C and then is discharged. According to the method disclosed by the invention, the problem of obvious reduction of the plasticity of steeland unqualified ultrasonic flaw detection due to white point tendency caused by separation of hydrogen during cooling of the electroslag type hydrochrome molybdenum steel is solved. The steel plate produced by the method contains pure steel and has the characteristics of dense internal mass and stable performance; the intensity and the toughness of a position which is 1/2 of the thickness of theplate achieve a good matching effect. The method is suitable for batch production of electroslag type hydro type steel plates, and is low in production cost and stable in mechanical property.