When cooked food are packaged in modified atmosphere package (MAP), the mixing ratio of fresh gas is: nitrogen (N2) 64% ~ 66%, carbon dioxide (CO2) 34% ~ 36%, gas replacement rate ≥98%. Since many microorganisms (bacteria) need O2 to grow and reproduce, reducing oxygen content can slow down the growth rate of bacteria (except anaerobic bacteria). The results showed that the reasonable mixture of N2 and CO2 formed a broad spectrum of bacteriostasis, color and taste protection layer on the food surface, and preserved cooked food under low oxygen environment. Therefore, when the error rate and replacement rate of gas mixing precision cannot reach the target, its bacteria-inhibiting and fresh-keeping effect is basically ineffective.