The invention provides graphene/silicon carbide nano-composite structure monolithic ceramic and a preparation method thereof, and relates to preparation of a ceramic material. The preparation method comprises the following steps: 1) synthesizing a precursor PCS(GOx); and 2) preparing the graphene/silicon carbide nano-composite structure monolithic ceramic SiC(rGOx). Precursor PCS(GOx) powder is prepared from raw materials comprising GO, VTES and PCS through a chemical modification method, and then the compact graphene/silicon carbide nano-composite structure monolithic ceramic SiC(rGOx) is obtained through the steps of compression molding forming and high-temperature pyrolysis. The VTES has a -Si-O-bond and a -CH=CH2 group, so the GO and the PCS can be compounded to generate a new GO-VTES-PCS macromolecular structure. The GO is compounded to the silicon carbide ceramic, so that the crosslinking area of the precursor can be enlarged obviously, formation of the SiC nano-crystal is inhibited, the sintering temperature is reduced, and the problems that the silicon carbide monolithic ceramic prepared by a precursor method is difficult to form and low in compactness are solved.