The invention provides a chitosan sericin compound finishing agent and a finishing method for cotton fabrics. A preparation method for the compound finishing agent comprises the following steps that 1), chitosan is dissolved; 2), chitosan is oxidized; 3), the finishing agent is prepared; the finishing method for the cotton fabrics particularly comprises the following steps that 1), cotton fabricsare pre-treated; 2), the cotton fabrics are soaked; 3), the cotton fabrics are subjected to after-treatment; under the microwave radiation, after a TEMPO oxidation system is adopted for conducting C6modifying treatment on the chitosan, the chitosan and sericin are subjected to covalent cross-linking to obtain a novel ecological textile dyeing and finishing auxiliary agent, higher stability is achieved regarding the environmental condition, and the novel ecological textile dyeing and finishing auxiliary agent cannot be easily heated and influenced by environmental changes; when a cross-linkingagent is not added, the compound finishing agent directly treats cotton fiber products, the cotton fiber products have antibacterial and wrinkle proof functions and good function durability, and after the cotton products are washed, the sericin loss rate can be better controlled; by adopting the compound finishing agent, functional modification of the cotton products meets multiple requirements of ecology, multi-functionality and durability.