The invention relates to a vacuum electron beam assembly welding process for a high-carbon-equivalent super-thick composite blank. The carbon equivalent of the high-carbon-equivalent super-thick composite blank is more than or equal to 0.5 %, and the thickness of a finished product of a steel plate is 150-450 mm. The vacuum electron beam assembly welding process for the composite blank includes the following steps: 1) selecting composite blank materials, 2) processing the composite blank materials, 3) preheating the composite blank, 4) conducting secondary surface cleaning, 5) preserving heatand conducting homogenizing, 6) welding the composite blank, and 7) conducting heating in a furnace after welding. In combination with the field production process flow of a steel plant, the vacuum electron beam assembly welding process for the high-carbon-equivalent super-thick composite blank is provided to solve the technical problem that welding microcracks easily appear in the welding processof the high-carbon-equivalent super-thick composite blank, thus the generation of the welding microcracks can be effectively avoided, and the low-cost stable production of high-carbon-equivalent super-thick composite plates is realized.