The reason for serious gap leakage and the damage of sealing part in a large slurry pump was speculated as the inappropriate design of sealing water.A 3dimensional numerical method,which is based on the equivalent liquid assumption,was used to solve the solidliquid two phase flow in the whole fluid domain (impeller,volute and watersealing chamber) of the slurry pump with kε EARSM turbulence model.The results indicate that the flow in the plate gap is obviously asymmetrical for the influence of the wall on both sides,the location of the blades and crosssectional area of volute.This explains the reason that the 1dimensional formula and the 2dimensional numerical method,both of which are based on the homogeneous distribution,cannot calculate the correct sealing water parameters.The responses of the sealing water pressure and the wasted power in plate gap to the change of volume flow rate are attained.According to the results,the reason for the failure of the sealing might be the shortage of the flushing water and the design defect on the part of volute where is from 10° to 40° before the tongue.The recommend value of the sealing water parameters and improving suggestion are provided.