The invention discloses an injectable bioadhesive, its preparation method and application, and belongs to the technical field of polymer materials and biomaterials. The present invention selects carbohydrate macromolecules with good biocompatibility—dextran and chitosan oligosaccharides as the matrix, mixes them with dopamine and an oxidative cross-linking agent and disperses them in an aqueous solution, and undergoes rapid gelation, that is, a multi-cross-linked biological adhesive. The bioadhesive material obtained in the present invention not only has injectability, is convenient for practical application operation, can be applied to skin tissue, and can inject the required amount according to the size of the required bonding, etc., and it has higher mechanical strength, no Cytotoxicity and excellent tissue adhesion performance, can be applied to the adhesion of various materials such as animal skin, internal tissues and organs, glass, metals and their oxides, sealants, plastics, etc. in clinical surgery. It has broad application prospects in fields such as fusion and repair, hemostasis, packaging, and sealing.