In the face of different market demands, civil aircraft usually have been changed business aircraft, remote sensing aircraft, sea surveillance aircraft and other special aircraft after obtaining the model certificate, through modification. Large range and long voyage are important features of many special aircraft. Civil aircraft usually add auxiliary fuel tank in cargo to increase the amount of fuel on board, so as to increase the range. However, the fuel in the auxiliary fuel tank does not supply the engine directly, so it is necessary to transfer the fuel in the auxiliary fuel tank to the basic fuel tank during the cruise phase, and supply the engine through the fuel supply system in the basic fuel tank. The transfer power can come from the transfer pump or the closed ventilation system, that is, the auxiliary fuel tank and the basic fuel tank produce a certain pressure difference, through which the fuel can be transferred to the basic fuel tank. However, different transfer port positions will lead to different control logic of fuel transfer. Based on the basic fuel tank configuration of a civil aircraft, the reasonable position of the transfer port is given by analyzing the position of different transfer ports in this paper.