Abstract: In this paper the freshly squeezed orange juice was inoculated in a certain amount of Saccharomyces cerevisiae,and then stored under different proportions of CO_2gas( 20%,40%,60%,80%).During the storage,the main composition conversion quantity of saccharides,acid,alcohol,aldehyde and the environment gas were measured. The effect of controlled atmosphere storage on the metamorphism of Saccharomyces cerevisiae inoculated fresh orange juice was investigated. Results showed that the effect of 20% CO_2 initial concentration on the juice Saccharomyces cerevisiae was weak,so the number of Saccharomyces cerevisiae was largest. In this condition,it resulted in the largest amount of saccharides consumption,and high yield rate of acid and alcohol relative to other groups.In 60% CO_2 group,the Saccharomyces cerevisiae in the juice was influenced and its main metabolite was alcohol. When the initial concentration of CO_2 was 40%,the main metabolite of Saccharomyces cerevisiae was acid. And in this case,this controlled atmosphere could restrain the bleeding of Saccharomyces cerevisiae,reduce the number of Saccharomyces cerevisiae and the consumption of saccharides. Besides,the environment gas CO_2 remained stable at the early stage under this condition,which was suitable for the preservation of fresh orange juice.