The invention discloses a lower fuel tank structure capable of guaranteeing normal fuel suction of a fuel pump. The lower fuel tank structure comprises a lower fuel tank, a three-way valve, a main fuel sucking pipe, a first fuel sucking branch pipe and a second oil sucking branch pipe. A fuel storage groove is concavely formed in the inner wall of the lower fuel tank, two fuel collectors which are connected with the inner wall of the lower fuel tank are arranged in the fuel storage groove, and the two fuel collectors and the lower fuel tank form fuel collecting grooves. The three-way valve is positioned in the fuel storage groove, one end of the main fuel sucking pipe penetrates the lower fuel tank and is connected with the three-way valve, and the first fuel sucking branch pipe and the second fuel sucking branch pipe are connected with the three-way valve, are oppositely connected to the other ends of the three-way valve and are respectively arranged in the two fuel collecting grooves. The lower fuel tank structure has the advantages that the lower fuel tank structure can assist the fuel pump to suck fuel, the fuel pump can assuredly normally suck fuel when the quantity of the fuel in a fuel tank is low and an automobile travels uphill and downhill, and accordingly potential safety hazards caused by the fact that the fuel pump cannot normally suck the fuel can be eliminated.