The concentration of chemical slurry such as sodium sulfate and sodium chloride after crystallization is about 15-20%. After being concentrated through Haiwang separator, the underflow concentration can be rapidly increased to more than 50%. The underflow concentrate enters the thickener and then enters the de-watering equipment such as centrifuge for drying, which reduces the operating load of de-watering equipment, improves the efficiency of de-watering equipment and evaporator, improves the operation cycle of equipment and reduces the power consumption.