The optimal initial gas composition (CO₂, O₂ and N₂) and its effects on quality and shelf-life of Pacific white shrimp (Litopenaeus vannamei) under controlled freezing-point storage at −0.8°C was determined through microbial flora, pH, total volatile basic nitrogen (TVB-N), exudates and sensory analyses. Pacific white shrimp under gas to product ratio of 3:1 and gas composition spanning the whole area from 0 to 100% based on a simplex centroid mixture design were analyzed after 2, 4 and 6 days of storage. Mesophilic and psychrotrophic bacteria counts, pH and TVB-N contents decreased and formation of exudates increased with increasing of CO₂ levels, but odor and appearance scores decreased and mesophilic and psychrotrophic bacteria counts, pH and TVB-N contents increased in the shrimp with decreasing CO₂ and increasing N₂ concentration. Besides, low O₂ levels could favor the odor of raw shrimp. Finally, The optimum gas composition for modified atmosphere packaged Pacific white shrimp under controlled freezing-point storage at −0.8°C was determined to be 75%CO₂, 10%O₂ and 15%N₂, and it could give the most suitable formation of exudates and lowest TVB-N and inhibit the growth of microbial flora; and at the same time maintain high odor and appearance scores in packaged Pacific white shrimp, and the shelf-life was extended to 11 – 12 days, which would be obviously beneficial for the exploitation of quality control, shelf-life extension and development of active packaging on shrimps.