Abstract:[Objective] Analysis microbial diversity of chilled beef with MAP (modified atmosphere packaging, 65% O2 and 35% CO2) and conventional packaging during storage (4?°C). [Methods] PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) of V3 area fragment of 16S rDNA and cloning analysis method of 16S rDNA were used to analysis the microbial diversity and dynamic changes of predominant bacteria in chilled beef with MAP and conventional packaging. [Results] Psychrobacter and Pseudomonas were the initial dominant bacteria. During storage, Pseudomonas and Brochothrix turned into the dominant bacteria in chilled beef with conventional and MAP packaging. The species of bacteria in beef with conventional packing were more abundant, and bacteria changed significantly at earlier storage. [Conclusion] The results showed a big difference in microbial community structure between two kinds of packing beef, and indicated that CO2 played a certain inhibitory action in beef with MAP.