The invention belongs to the technical field of high-molecular materials, and discloses a modified organic silicon adhesive and a preparation method thereof. The organic silicon adhesive provided by the invention is prepared from the following components in parts by weight: 15 to 20 parts of amine compound, 20 to 25 parts of epoxy resin compound, 20 to 30 parts of polysiloxane, 2 to 4 parts of toughening agent, 0.001 to 0.005 part of platinum catalyst and 1 to 2 parts of curing agent. The modified organic silicon adhesive contains both the amine compound component and the epoxy resin compound component, and an addition reaction is performed on the amine compound and the epoxy resin compound to modify the epoxy resin compound, so that the cured adhesive has very high bonding strength, also has high thermal stability, and can be widely applied to the industries of aerospace, ships, automobiles, electronic products, construction and the like.