The invention discloses a polarizer based on a graphene/polymer mixed waveguide structure and a preparation method thereof, and belongs to the technical field of polymer planar optical waveguide devices and preparation thereof. According to the invention, a silicon wafer is used as a substrate, organic polymer materials are respectively used as cladding and core layer materials of an optical waveguide, by utilizing the advantages of simple and flexible processing technology and the like of the organic polymer materials, the graphene film is buried in the polymer optical waveguide, so that theinteraction between an optical field in the waveguide and the graphene film is fully improved, and one type of polarized light is filtered according to the absorption characteristic of the graphene material to different types of polarized light. The preparation method provided by the invention is relatively simple, only needs some common semiconductor equipment and conventional manufacturing processes, does not need complex and expensive process equipment and a high-difficulty preparation technology, is compatible with a traditional semiconductor process, is easy to integrate and suitable forlarge-scale production, and thus has important application prospects.