In order to research the scrubbing inerting process in multi-bay fuel tank of an aircraft, scrubbing gas was transformed into two sections, fuel mass transfer section and no-mass transfer section. By theoretical calculation, fuel was in mass transfer with scrubbing gas and the amount of oxygen escaped to the gas phase space was obtained. The no-mass transfer section could be used to access the gas space directly considered as fuel washing process. The other section could be combined to build the model for engineering calculations by working out the amount of oxygen spilling from fuel. In this way, the whole scrubbing inerting process was transformed into washing process with escaping gas. The results show that the model for the conversion of scrubbing inerting to washing with overflow is really credible. The results of the model are consistent with experiment results. As time increases, the gas phase oxygen volume fraction will increase and then decrease again, converging to a final gas phase oxygen volume fraction equal to the value of the scrubbed gas. The result of multi-bay fuel scrubbing shows the time required for stabilizing is related to the distance from the inlet and the volume of each bay. ©, 2015, BUAA Press. All right reserved.