The work aims to study the effect of mass fractions of purple tomato anthocyanin (PTA) on the performance of composite films and to test the color response of composite films to different pH values. With chitosan (CS) as the base material and PTA as the additive, composite films with PTA mass fractions of 0, 1%, 3% and 5% (the percentage of PTA relative to CS) were prepared by solution blending method. The effects of PTA mass fractions on the contact angle, tensile strength and water vapor transmission rate of the composite films were investigated, and the pH sensitivity of the composite films was examined by the color response to different pH values. PTA showed purplish red color in acidic environment and became lavender transparent and was close to colorless transparent in neutral environment, and showed orange-yellow color in alkaline environment. The performance of PTA/CS composite films with different mass ratios (mCS∶mPTA) was tested, and it was found that the addition of PTA reduced the hydrophilicity of the composite films, but the tensile strength and elongation at break increased significantly. The color change of the PTA/CS composite films with high concentration was less obvious under acidic conditions, and the color of the composite films became yellow significantly under alkaline conditions. The addition of a certain amount of PTA can improve the mechanical properties of the films and enhance the hydrophobicity. If the pH sensitivity of PTA/CS composite films can be improved, combined with the fact that PTA/CS composite films have many excellent properties, it can provide a certain theoretical basis for the preparation of high-performance chitosan-based food packaging materials.