The invention discloses a sealing method of a vacuum compressor in the process of making natural gas into acetylene. Gas at the vacuum compressor outlet is separated in a gas liquid separator, a liquid phase separated by the gas liquid separator enters a solvent buffer tank through a liquid level adjusting valve of the gas liquid separator, an emptying pipe on the top of the solvent buffer tank discharges air, a solvent in the solvent buffer tank is cooled by being fed into a solvent cooler through a pump, and a part of the cooled solvent enters the vacuum compressor for cooling gas while theother part is fed into a machine seal of the vacuum compressor as a sealing medium. The sealing method disclosed by the invention fully fits sealing of the vacuum compressor in a device of making natural gas into acetylene. A part of the cooled liquid phase of the gas liquid separator at the vacuum compressor outlet is fed into the machine seal of the vacuum compressor as the sealing medium, so that the sealing demand can be met, and desalted water is not added into a solvent system. Therefore, the energy consumption and the material consumption are reduced, and the operating cost of the device is lowered.