The invention discloses postoperation anti-adhesion hydrogel and a preparing method thereof. The hydrogel is prepared from sodium alginate powder, chitosan powder, acrylamide monomers, N,N'-methylene bisacrylamide, calcium sulfate, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine. The preparing method of the high-strength high-tenacity chitosan and sodium alginate compound hydrogel is easy to operate, parameters are controllable, the materials are easy to obtain, and the solvent is nontoxic or low in toxicity and safe to treat and use; the method integrates advantages of the two natural biological materials, and the requirement for postoperation adhesion prevention of patients and the requirement for nursing care and treatment of medical workers can be met well. The hydrogel is soft, can be attached to the skin easily, has good flexibility and can effectively prevent wound surface adhesion and be degraded and absorbed, secondary trauma is avoided, and the hydrogel is expected to become a novel postoperation anti-adhesion material.