The invention discloses a device for preparing a boron-doped diamond composite coating on the surface of a cutter, belonging to the technical field of cutters. The device comprises a reaction hood, an alloy drilling bit, a supporting table, a cooling device, a direct current voltage bias power supply, a heat wire power source, air pressure control device, a high-temperature resistant spring, a heat wire and a drilling bit bracket, wherein the alloy drilling bit and the high-temperature resistant spring are respectively and vertically arranged on the drilling bit bracket; two ends of the heat wire are respectively connected with the high-temperature resistant spring; the drilling bit bracket is fixed on the supporting table and the cooling device; the reaction device is fixed on the supporting table and the cooling device and the outer part of the drilling bit bracket is connected with the air pressure control device; the direct current voltage bias power source is respectively connected with the heat wire and the shell of the reaction hood; and the heat wire power source is respectively connected with the heat wire and the high-temperature resistant spring. The invention can ensure excellent adhesive strength between a diamond composite film and a matrix and can effectively improve the surface quality and the uniformity of the diamond film, thereby improving the service life and the cutting performance of the cutter with the diamond film coating.