The invention provides a method of producing a super-thick steel plate by compounding and welding continuous casting slabs. The surface cleaning is carried out, specifically, the processed continuous casting slabs are wiped with industrial alcohol and the surfaces of the continuous casting slabs are blown with clean compressed air; then grooves are polished along two long sides of the combining surface of the lower continuous casting slab; the continuous casting slabs are assembled to form a composite slab by using a slab turning machine and an aligning unit; spot welding is performed on welding seams in starting positions of the grooves, and then continuous welding is performed on the welding seams of the grooves; after the composite slab is conveyed to a vacuum chamber, a part which is not welded is welded by virtue of a rotary workbench in the condition that air pressure is 5*10<-3> Pa; after the composite slab is heated by adopting a chamber type heating furnace, the composite slab is rolled, the rolling temperature is 900 to 1100 DEG C, the rolling reduction in horizontal pass is 15 to 20 mm, the rolling reduction in longitudinal pass is greater than or equal to 40 mm, the rolling speed is 0.8 to 1.5 m/s; and after rolling, the composite slab is directly stacked with a hot steel plate and is slowly cooled for 47 to 50 h. According to the method, the spot welding in the vacuum chamber can be reduced, the production capacity of the vacuum chamber is increased by 2 to 3 times, and the method has the characteristics of low energy consumption, low cost, high efficiency, high yield and high quality.