The invention relates to a silicon dioxide filled PTFE composite and a preparing method thereof to prepare PTFE engineering materials with a low dielectric constant and low density, and especially belongs to the field of light composites. According to the preparing method, colloid carbon spheres serve as a template, a surfactant CTAB is added at the same time to improve the reaction efficiency, and hollow silicon dioxide nanometer spherical particles are prepared under the strong basicity condition; then, the particles serve as filling particles filling a PTFE composite, and finally the hollow silicon dioxide nanometer spherical particle filled PTFE composite is obtained. According to the silicon dioxide filled PTFE composite prepared through the method, the dielectric constant is low and ranges from 2.1 to 2.8, and the density is low and ranges from 0.8 g/cm<3> to 1.2 g/cm<3>; according to silicon dioxide for filling the PTFE composite, the specific surface area ranges from 700 m<2>/g to 900 m<2>/g, the particle size is uniform and ranges from 400 nm to 1 micrometer, a hollow spherical structure is formed, the spherical shell thickness ranges from 40 nm to 80 nm, the sphericity is high, and preparation efficiency is high.