Abstract: The effect of pH values on the tensile strength,opitical property,and water vapor permeability of soy bean proteinisolate -carboxymethyl cellulose composite materials were evaluated. The composite materials at pH10 showed the highest tensile strength,excellent transparence,and ultraviolet -blocking preformence. The FT-IR showed the strech vibration of C-N was reduced when the pH raised,which was one of the reason for the tensile strength improvement.