Abstract: In order to inhibit melanosis of Pacific white shrimp and prolong its shelf-life, 1% chitosan was combined with a kind of mixed anti-melanosis component (M) to prevent corrosion of Pacific white shrimp under modified atmosphere packaging (MAP) of two gas mixtures, i.e., 40% CO2 /30% O2 /30% N2 (Ⅰ) and 85% CO2 /5% O2 /10% N2 (Ⅱ) with high-barrier packaging bag (K-PET/PE) at (4±1)℃. Total bacteria count (TBC), total volatile basic nitrogen(TVB-N), pH, polyphenol oxidase (PPO) activity, and sensory evaluation were determined to evaluate the effects of the different preservation methods. The mixed anti-melanosis component (M) were optimized by orthogonal experiment, the optimal combination was as follows, 0.01% 4-hexylresorcinol+1.5% citric acid+1% ascorbic acid, the Group (Chitosan+Ⅰ), (Chitosan+M+Ⅰ), (Chitosan+Ⅱ) and (Chitosan+M+Ⅱ) began to generate melanosis dramatically at 6th, 8th, 12th and 14th day, respectively; all treatment groups, compared with the control, could slow down the increase of TBC, TVB-N, PPO activity and the pH significantly during the whole storage period. The fresh-keeping effect of Group (Chitosan + M + Ⅱ) was the best in all groups, extending the shelf-life of Pacific white shrimp more than two times compared with control when stored at (4±1)℃. Film-forming combined with modified atmosphere packaging is an effective preservation method for Pacific white shrimp, which has application values.