A simple packaging device with perforations was set up. CO2 was used as experimental gas. Dynamical CO2 concentration in the package was theoretically analyzed and practically measured. Results showed that practical measurement of CO2 concentration in the package were much higher than theoretical analysis. The results were explicated as perforation end effect, and meanwhile the corrective formula of effective length of perforation in the film was put forward, which was def =d+7r /6.