The invention provides a preparation process of an ultrathin rock plate. The process comprises the following steps: S1, preparing raw material powder, namely putting corundum, quartz, potassium feldspar, albite and polycrystalline mullite fibers into a ball mill according to a ratio, and carrying out ball milling; S2, powder distribution: after magnetic separation for iron removal and homogenization, adding a toughening agent and an activating agent into the powder in proportion, drying, spraying and granulating in a drying sprayer to form a mixture, and then feeding the mixture into a distributor for distribution; S3, high-pressure compression molding, specifically, conveying the powder obtained in the step S2 into a ceramic plate mold through a conveying belt, carrying out compression molding through a 500-ton air pressure vibration molding machine, and manufacturing a green body of the ceramic rock plate; S4, spraying glaze; S5, ink-jet printing; S6, coating a bottom slurry of the brick; S7, firing specifically, firing the ceramic rock plate; and S8, carrying out detecting, sorting and warehousing. The preparation process of an ultrathin rock plate is high in toughness, attractive in appearance and not prone to embrittlement.