The three effect evaporator is mainly composed of three sets of evaporators, condensers, salt separators and auxiliary equipment in series with each other. The three sets of evaporators operate in series and form a three effect evaporator. The complete evaporation system adopts continuous feeding and continuous discharging. Waste water first enters into effect forced circulation evaporator with high salt crystallization, crystallization of the evaporator with a circulation pump, the wastewater into the heat transfer chamber, a heat exchange chamber in evaporation, external vapor generated latent heat of vaporization, heat of waste water. As the evaporation heat transfer chamber pressure is greater, the waste water in the evaporation heat exchanger room is heated above the normal liquid boiling point pressure to overheating. When the heated liquid enters the crystal evaporation chamber, the pressure of the waste water drops rapidly, resulting in partial waste water flashing or boiling rapidly. After the evaporation of the wastewater, the steam enters the two effect forced circulation evaporator and is used as the power steam to heat the two effect evaporator without evaporating. The waste water and the salt exist temporarily in the crystal evaporation chamber. One effect, two effect and three effect between the forced circulation evaporator communicated by balance pipe under the action of negative pressure, high salinity wastewater flow by two to turn effect effect, three effect, wastewater has been evaporated, more and more high concentration of salt water, when the water salinity in the over saturated state. Salt water will continue to set the lower part of the room into the salt precipitation, evaporation and crystallization of the room. Salt absorption pump will continue to waste water containing salt to the salt salt in the vortex separator, vortex separator, solid salt is separated into the storage ponds. The separated waste water into two effect forced circulation evaporator heating, the whole process cycle, to achieve the ultimate separation of water and salt. The condenser is connected with a vacuum system, and the vacuum system extracts the non condensing gas produced in the evaporation system, so that the condenser and the evaporator keep the negative pressure state, and the evaporation efficiency of the evaporation system is improved. Under the influence of negative pressure, the two steam produced by the waste water in the three effect forced circulation evaporator automatically enters the condenser. Under the cooling of the circulating cooling water, the two steam produced by the waste water rapidly turns into condensed water. Condensate can be recycled to the reuse tank by means of continuous water discharge.