The displacement characteristic curve of water drive is still used in CO2 immiscible flooding. There are not standard displacement characteristic curve and mathematic description method for gas drive. Piecewise relations were theoretically derived to determine the relationship between cumulative gas production and cumulative oil production. Based on displacement characteristics，the displacement characteristic curve of CO2 immiscible flooding for low permeability reservoir was obtained. Combined with laboratory experiments and pilot tests，the double logarithmic piecewise linear relations were proved effective to explain displacement characteristics of CO2 immiscible flooding. The constants of the linear relations can be regressed through production data. And they can also be used to predict the effects of CO2 immiscible flooding. Additionally，gas channeling time can be obtained by the gas displacement characteristic curve. The adjustment measures can be determined quickly through the relations. Pilot tests of CO2 immiscible flooding in Yaoyingtai Oilfield show that the gas channeling happened 12 months after gas injection. According to the gas displacement characteristic curve，the slope of gas channeling section decreased sharply after WAG applied. And the extent of gas channeling was reduced.