Sealing method for performing single sealing on packaging bag by using vacuum sealing machine

The invention provides a sealing method for performing single sealing on a packaging bag by using a vacuum sealing machine. The vacuum sealing machine comprises a cover plate assembly, wherein the cover plate assembly is provided with a control panel, a heat sealing device and a vacuumizing device, the heat sealing device and the vacuumizing device are electrically connected with the control panel, the cover plate assembly comprises an upper cover assembly and a lower cover assembly, and the upper cover assembly covers the lower cover assembly and is movably connected with the lower cover assembly. The sealing method at least comprises the steps that a sealing step is carried out, specifically, the control panel controls the heat sealing device to be started to seal the packaging bag; a pre-tightening step is carried out, specifically, the control panel controls the vacuumizing device to be started to perform a vacuumizing action so as to pre-tighten the cover plate assembly and the packaging bag; the executi