The invention discloses a method for processing and producing jackets for writing brushes. The method is implemented by a device for processing and producing the jackets for the writing brushes. The device comprises a machine and a first cavity. The first cavity is arranged in the machine, a second cavity which is positioned at the lower end of the first cavity is arranged in the machine, an injection channel is arranged at the upper end of the machine in a communicated manner, a first groove is formed in the inner wall of the right end of the first cavity, a fixed mold plate is fixedly connected with the inner wall of the right end of the first cavity, a liquid accommodating bowl which is positioned at the lower end of the injection channel is connected with the upper end surface of the fixed mold plate in a running fit manner, a sprue bush is arranged on the fixed mold plate in a communicated manner, a main runner which is used for being connected with the sprue bush is connected with the lower end surface of the fixed mold plate in a running fit manner, a rotary valve is peripherally connected onto the main runner in a slide fit manner, and a gear disc which is positioned at thelower end of the rotary valve is fixedly connected onto the main runner and is connected with the rotary valve in a threaded manner. The method has the advantages that the method is high in linkage property, the production quantities can be increased by a mold and four cavities, and the plastic part molding efficiency can be enhanced by additional water cooling.