The invention relates to a novel antimicrobial film forming liquid medical dressing. The novel antimicrobial film forming liquid medical dressing is prepared from, by weight, 85-96 parts of purified water, 0.5-10 parts of modified chitosan, 0-10 parts of alginate, 0-10 parts of natural plant purple pigment and a proper quantity of auxiliaries. The novel antimicrobial film forming liquid medical dressing has the advantages that the biological antimicrobial film forming liquid medical dressing prepared through the method is suitable for various wounds and is an external dressing, a non-medicine and non-macro ion reticular membrane can be formed when the dressing is sprayed to the skin or the mucosa or the wound surface, the physical antibacterial effect and the invisible gauze effect can be achieved, and the adhesion is high; infection can be isolated while the long-acting antibacterial effect can be achieved, and the medical dressing is a novel nursing material having the advantages of having biocompatibility, safety, adhesion prevention, bacterial resistance and hemostasis, promoting wound healing and the like. When the medical dressing is used in cooperation with a wet wound protection dressing, the wound is prevented from making contact with the environment, external infection is avoided, and healing of the wound is promoted.