The principle of multi-effect evaporation is to connect multiple evaporators in series, the secondary steam of the former evaporator is used as the heating steam of the next evaporator, and the heating chamber of the next evaporator is the condenser of the previous evaporator. In the multi-effect evaporation system, only fresh steam needs to be added at the first effect, and the secondary steam generated at the top of the first effect evaporation tower is directly used as the heating medium for the reboiler of the subsequent first-effect evaporation tower, and the fresh steam does not need to be introduced into the evaporation tower after the first effect, and the steam at the top of the last effect tower can be used as a low-pressure heat source. Therefore, its greatest advantage is the repeated use of secondary steam vaporization and condensation, which can significantly reduce fresh steam consumption.