The invention discloses a highly-heat-insulating highly-light-transmitting high-strength polymethylmethacrylate composite material and a preparation method thereof. Silicon dioxide aerogel serving as a super heat-insulation material and flaky nanomaterial graphene are adopted to be subjected to surface chemical state regulation and are composited with a PMMA (polymethylmethacrylate) bulk polymerization system to prepare the composite material, the graphene and PMMA form pi-pi conjugation interaction alternately, and the prepared polymethylmethacrylate composite material with the silicon dioxide aerogel and the graphene being functionalized synergistically is high in strength, heat insulation and light transmission and the like. The highly-heat-insulating highly-light-transmitting high-strength polymethylmethacrylate composite material and the preparation method thereof have the advantages that since the silicon dioxide aerogel and the functionalized graphene synergize to serve as a PMMA functionalized phase, tensile strength, heat insulation performance and visible light transmittance of the PMMA can be enhanced synergistically, and conditions are created for popularizing the PMMA to the field of heat insulation of transparent building envelopes.