The invention relates to a liquid-solid separation method for treating gypsum serum, which comprises: pumping the gypsum serum to be treated into a novel hydrocyclone through a pump from a liquid storage tank, obtaining gypsum suspension with high solid content after separation, exhausting and collecting the gypsum suspension from a desilting nozzle of the novel hydrocyclone, exhausting light phase from a liquid outlet section of an overflow center hole of the hydrocyclone to a wastewater disposal basin, and exhausting slightly heavy phase from a liquid outlet section on an overflow side faceand returning the slightly heavy phase to the liquid storage tank for recycling. The liquid-solid separation method controls the system pressure and the flow rate by adjusting a valve, and makes various flow rates in the optimum state. Compared with the prior art, the liquid-solid separation method has the characteristics of low cost, high efficiency and environmental protection.