Abstract: To investigate effects of composite biopreservative on maintaining freshness and quality of half shell oysters, a mixed preservative composed of chitosan∶lysozyme∶tea polyphenol（1∶0.5∶0.5）was selected to treat oysters．At 4 °C refrigeration conditions, changes in sensory evaluation, total volatile base nitrogen, total bacterial account, pH, glycogen, protein, Ca²⁺-ATPase, and malonaldehyde were measured in half shell oysters．Results demonstrated that composite biopreservative could effectively maintain oysters sensory quality, delay pH changes, inhibit bacterial growth and proliferation, and extend shelf life of half shell oysters from 6 days to 12 days．Moreover, it could effectively maintain oysters quality, decelerate glycogen decomposition, reduce protein decomposition rate and fat oxidation rate．Composite biopreservative application will provide a reference for preservation of oyster products．