The invention discloses a single-component epoxy modified silicone sealant and a preparation method thereof. the sealant is composed of, by mass, 100 parts of silane modified polyether resin, 10-50 parts of epoxy resin, 80-150 parts of plasticizers, 150-300 parts of nano calcium carbonate, 1-6 parts of first cross-linking agents, 3-10 parts of second cross-linking agents and 2-7 parts of catalysts. The advantages of the epoxy resin and the silane modified polyether resin are combined, the bonding powder, the tensile strength, the elasticity and the weather resistance of the sealant can be improved, and the sealant can be used for the different fields such as constructional engineering, electronics, the automobile industry and space flight and aviation. The sealant has the characteristics that the performance advantages of silicone and the epoxy resin are combined, the silicone and the epoxy resin are subjected to a cross-linking reaction with water molecules and the cross-linking agents under the action of the catalysts, and a three-dimensional spatial netty structure is formed. A cured system is high in binding performance and excellent in mechanical performance and weather resistance.