The invention relates to an 
evaporator, and a control method for vacuum degree, 
evaporation kettle liquid level and water tank 
water level detection. The method comprises: starting a 
system; detectingthe liquid level of a waste liquid 
barrel; determining whether the liquid level is low or not, if yes, controlling, by a PLC, a circulating water pump to be closed and turning on an emptying valve, and otherwise, controlling, by the PLC, the circulating water pump to start, and turning on a liquid 
inlet valve so that the circulating water pump runs to turn the pressure in an 
evaporation kettle tobe negative pressure; determining whether the vacuum degree is larger than a set value or not, if yes, starting a compressor so that a 
refrigerant starts to circulate, and otherwise, returning; sucking a 
stock solution into the 
evaporation kettle through the liquid 
inlet valve under negative pressure, and detecting the liquid level of the evaporation kettle by a sensor; if the liquid level is higher than the high liquid level, controlling the liquid 
inlet valve to be turned off by the PLC in the evaporation kettle; if the liquid level is lower than a low liquid level, determining whether thenumber of times of liquid supplementing is larger than a set value or not by the PLC, if not, controlling the liquid inlet valve to be turned on by the PLC and returning, and if yes, controlling the emptying valve and the liquid discharging valve to be turned on by the PLC, starting a liquid discharging pump, turning off the compressor and the circulating water pump, after concentrate is discharged after set time, turning off the emptying valve, the liquid discharging valve and the liquid discharging pump and returning.