The invention discloses a hot rolling compounding method of a steel/aluminum composite thick plate. The method comprises the following preparation steps: (S1) steel plates and aluminum plates are prepared; (S2) intermediate layers are coated on the surfaces of the steel plates; (S3) four layers are symmetrically assembled as a blank; (S4) the blank is heated and insulated; (S5) the hot rolling compounding is performed; and (S6) the trimming and the stripping are performed. Through the modes of coating of the intermediate layers on the surfaces of the steel plates and symmetrical assembly of the blank by four layers, the problems of low interface combination strength and warpup caused by higher mechanical performance differences between steel and aluminum in an ultrathick plate state in a traditional hot rolling compounding process, namely main concentration of the deformation on the aluminum plates and no deformation of the steel plates are solved, the product quality and the production efficiency are prominently improved, and the industrial production is met.