The invention provides a substance balance method for predicting carbon dioxide flooding oil reservoir indexes. The substance balance method for predicting the carbon dioxide flooding oil reservoir indexes comprises the following steps of: 1, giving application conditions of a carbon dioxide flooding substance balance equation; 2, building a substance balance equation applicable to the carbon dioxide flooding; 3, storing oil reservoir parameters and determining a calculation parameter; 4, calculating the parameters of the corresponding time period, wherein the parameters of the corresponding time period include the oil yield and the gas injection volume; and 5, using the parameters obtained through the calculation in the fourth step to determine the carbon dioxide flooding oil reservoir indexes such as the injection-production ratio and the recovery percent. The substance balance method for predicting carbon dioxide flooding oil reservoir indexes has the advantages that the substance balance equation which considers the compressibility of the oil reservoir rock fluid and is applicable to the carbon dioxide flooding is built; an application method of the substance balance equation is given; and an effective method is provided for predicting the carbon dioxide flooding oil reservoir indexes.