The invention discloses a spinning head and a method for preparing a braided tube/polymer composite membrane by using the spinning head. The spinning head comprises a shell and a cover plate, wherein the cover plate is arranged at the top part of the shell; the cover plate is provided with a fiber braided tube inlet, a pressurizing hole and a film casting liquid inlet; the fiber braided tube inlet is connected with an internal catheter extending to the bottom part of the shell; the bottom part of the shell is provided with a film casting liquid outlet; the film casting liquid outlet is connected with a spinning jet; the shell is of a double-layer cask-shaped structure; an inner layer cask forms a film casting liquid cavity; a cavity between an outer layer cask and the inner layer cask forms a circulating bath heating cavity; and side walls of the outer layer cask are respectively provided with a circulating bath inlet and a circulating bath outlet. According to the spinning head disclosed by the invention, through the centralized positioning and pre-coating action of the internal catheter and a braided tube channel on the spinning jet on the braided tube, the evenness of a polymer coating on the surface of the braided tube is effectively improved, and a binding force between the braided tube and the coating is enhanced. Moreover, the discharge rate of film casting liquid is controlled through nitrogen pressurization, and thus, the coating uniformity can be further ensured. The prepared braided tube/polymer composite membrane is higher in mechanical strength and burst pressure.