The present invention specifically relates to a storage tank vacuum-pumping device and a method for keeping long-time food fresh utilizing the storage tank. The storage tank vacuum-pumping device comprises a shell, a seal ring, an air pumping assembly, an electric switch key, an air exhaust valve button, a pressure valve, a pressure valve spring and a pressure valve linkage switch, wherein the seal ring is fixed at the bottom of the shell; an air inlet pipe of the air pumping assembly is in communication with the storage tank, and the air pumping assembly is electrically connected with the electric switch key; both the electric switch key and the air exhaust valve button extend out from the top of the shell; a first closed pipeline which is in communication with the storage tank is arranged in the shell, the pressure valve is installed in the first closed pipeline, and the pressure valve spring is fixed between the first closed pipeline and the pressure valve; and the pressure valve linkage switch is aligned with the pressure valve, and the pressure valve linkage switch is connected with the electric switch key in series. In the present invention, by the automatic control of the pressure valve and the pressure valve linkage switch, the storage tank can keep a vacuum state for a long time, and then effectively keep food fresh for a long time.