To realize a stable and controllable catalytic inerting process in the aircraft fuel tank, based on the process of the oxygen-consuming catalytic inerting system, using the gas composition in the ullage of the fuel tank as the benchmark, a mathematical model of the system process is established with reference to the mass conservation and energy conservation equations. By figuring out the relationship between stable oxygen concentration and flow rate, a stable oxygen concentration characteristic model is proposed, showing the internal relationship between stable oxygen concentration and different performance parameters like flow rate, heat generation rate, and water production rate. The results reveal that there is a flow ratio interval where the stable oxygen concentration remains steady at 0%, and the stable oxygen concentration in this interval does not change when the flow ratio changes. Furthermore, the interval grows as the catalytic reactor efficiency increases. The increase of the stable oxygen concentration can effectively reduce the catalytic reactors heat generation and water production rates. Under the present calculation conditions, the stable oxygen concentration tends to increase from 1% to 9%, and the heat generation and water production rates decrease by 36.1%. The relationship between the stable oxygen concentration and the flow ratio is affected by the fuel type: With the higher vapor pressure, greater flow ratio is needed to maintain the same stable oxygen concentration. The altitude and aircraft climbing rate may affect the stable oxygen concentration. In the case of a constant flow ratio, stable oxygen concentration decreases with the increase of altitude, and a greater climbing rate may lead to a faster decline rate of stable oxygen concentration.