Objective To optimize the fabrication process of chitosan (CS) and soy protein isolate (SPI) composite films, enhance their comprehensive performance, and evaluate their impact on the preservation of mangoes.Methods CS and SPI were used as the film-forming substrates. The tensile strength, elongation at break, water vapor transmission rate, oxygen permeability, carbon dioxide permeability, and light transmittance of the composite film were used as evaluation indexes. The K-value of the composite film's comprehensive performance was calculated using fuzzy comprehensive evaluation. Response surface analysis was applied to optimize the formulation of the CS-SPI composite film, with the K-value as the response variable.Results The optimal preparation conditions for the CS-SPI composite film were as follows: 1.9 g/100 mL of CS, 22.7 mg/mL of SPI, and 2.2 g/100 mL of glycerol at pH 2.9. Under these conditions, the K-value of the CS-SPI composite film reached 0.904. The internal network structure of the composite film was denser, effectively preventing the migration of water and gases. When applied to mango preservation at room temperature, the CS-SPI composite film extended the shelf life of the mangoes to 15 days.Conclusion The CS-SPI composite film prepared with the optimized process exhibited significantly improved comprehensive performance and demonstrated excellent preservation capabilities for mangoes.