In our work, a unique saucer structure of graphene aerogels in the form of graphene sheets (nearly 10 m) is designed to grow them in situ on hollow silica spheres that are connected to their neighbors by C-O and C-Si bonds after fabrication by spark plasma sintering (SPS). The graphene-silica porous ceramics (GSPCs) are characterized by Fourier transform infrared (FTIR), Raman and X-ray photoelectron (XPS) spectroscopies. The mechanism of metal-catalyst-free method for the direct synthesis of graphene aerogels in the form of large-size graphene sheets on hollow spheres is studied. Compared to other ceramics, GSPCs have an ultralow thermal conductivity (0.054-0.057 W m(-1) K-1 at room temperature (RT) and 0.038 W m(-1) K-1 at 90 K) and a relatively high compressive strength (7.4 MPa), which depends on the special saucer structure of the graphene aerogels and their high porosity (89.63%). We additionally find that the temperature dependence of the thermal conductivity is altered by the content of graphene aerogels.