Abstract: In the paper,a series of chitosan- gelatin- octadecoic acid compodite films with different ratios were prepared by blade casting process.The composite membrane were determinated with tensile strength,water vapor permeability as main index.The result showed that the addition of octadecoic acid could obviously improve water vapor permeability of blend membrane although the tensile strength fall slightly.And tensile strength was 56.0 MPa,water vapor permeability was 4.01E- 8 g·cm / cm2·s·Pa when the optimal blending ratio of chitosan/gelatin was7∶3,the optimal blending ratio of chitosan / octadecoic acid was 4 ∶ 1,the optimal blending concentration of acetic acid was 3%,the optimal blending drying temperature was 50 ℃.