Aiming at the limitations of the characterization of gas channeling strength at present, the gas channeling coefficient is defined by analyzing the dynamic gas ratio curves of CO2 flooding in tubes. Natural gas flooding experiments are conducted to verify the precision of the defined coefficient, and the results show that the precision could be as high as 0.03, the defined coefficient could be used to preliminarily evaluate gas channeling during gas flooding. The results also show that the defined coefficient is highly sensitive to displacement efficiency, approximately 0.015 change would be induced by per unit change in displacement efficiency.