Abstract: Abstract: Egg quality depends strictly on the storage environment after acquisition. The concentration of CO2 has an important influence on the respiration and freshness of eggs during storage. This study aims to further observe the diffusion and freshness changes of CO2 released from egg respiration under different CO2 concentrations. The respiration intensity and freshness of stored eggs were measured at the temperature of 25°C, the relative humidity of 65%, the CO2 volume fraction of 1.5%, 3.0%, 4.5%, and air (control group). The egg model was built by UG software. An ICEM CFD software was utilized to establish the fluid domain of the egg released carbon dioxide diffusion, and then divide it into a structural grid. A FLUENT software was selected to complete the diffusion simulation of the first day breathing release CO2 from eggs with different CO2 concentrations. The results show that the law of heavy gas diffusion was followed by the diffusion process of CO2 released from eggs with different CO2 volume fractions. Four stages were divided into: the initial, descending, mixing, and turbulent flow. The diffusion time in each stage was affected by the concentration of external CO2. Specifically, the diffusion amount and speed of CO2 released by egg respiration gradually decreased, with the increase of CO2 concentration in the storage environment. Egg respiration was inhibited, as the outside CO2 concentration increased. There was a significant difference in the respiration intensity and freshness of eggs stored in the external environment with the CO2 volume fraction of 1.5%, 3.0%, and 4.5% (P<0.05) during the entire storage. The inhibitory effect on the respiration intensity of the egg was no longer obvious, and the freshness remained unchanged (P>0.05) when the CO2 volume fraction reached 3.0%. The freshness level of eggs was still above the AA level, when stored under the environment of CO2 volume fraction of 3.0%, and 4.5% for 20 d. Taking economic factors into account, the CO2 volume fraction of 3.0% was better to achieve the optimal freshness of eggs during storage. This study provides new ideas and data support for modified atmosphere preservation of eggs.