The invention discloses a backwater system and a backwater method of a liquid ring vacuum pump. The backwater system comprises a vacuum pump body (1) and an external gas-water separator (8). The backwater system is characterized in that the other end of the gas-water separator (8) is connected with a heat exchanger (9), a booster pump (10) is connected to the tail of the heat exchanger (9), a plurality of pipelines are connected to the booster pump (10) and are connected with a backwater inlet (10.1) in the cylinder wall of the vacuum pump body (1), a flow monitoring device (11) is connected to each pipeline, and a pressure monitoring device (12) is connected to the pipeline behind the booster pump (10). The defect that cavitation easily occurs in a cavity due to the limit to the temperature and vapor pressure of working liquid in prior art is overcome, and the backwater system has the advantages that the working liquid is effectively supplemented, and the temperature of a liquid ring is reduced.