To visually monitor the CO2 concentration in food packaging, CO2 sensitive indicators (Methyl Red and Bromothymol Blue) were prepared by dissolving Methyl Red and Bromothymol Blue with concentration of 0.1% (w/w) in ethanol solution (50%, v/v). Glycerin and methyl cellulose were the main binder materials for preparing ink. The “Ink color-pH-CO2”correlation model was established. The detection effect of CO2 indicating ink was verified by storing oyster mushroom in a package, while the discoloration effects of ink and indicating solution were compared. The results showed that a water-based CO2 indicating ink was prepared with a mass ratio of 3:2 of Methyl Red and Bromothymol Blue, an added glycerin volume ratio of 4 % (v/v), and a methyl cellulose addition of 1.72 % (w/w). It was verified that the ink could be printed directly on the plastic film as per screen printing. With different CO2 concentrations (0 ~ 100 %), the color of indicating ink changed markedly. The color respond of indicating ink in oyster mushroom package was consistent with the color change of the indicating solution. The results calculated by established “Ink color-pH-CO2” correlation model were basically in conformity with the experimental ones. It was concluded that under certain condition of humidity, the indicating ink could visually display the concentration of CO2 in the package.