A suspension with good rheology and high stability is crucial for slip casting and gelcasting technology. However, a mixed suspension from two or more different powders usually has bad rheology because of the easy agglomeration of mixed powders caused by the attractive force between the powders with heterocharges. We studied the surface modification of the each single-component powders (SiC, Al2O3, ZrO2(3Y) powders) and the SiC-Al2O3-ZrO2(3Y) mixed powders to increase the repulsive force by adjusting the pH value and adding polyacrylic acid (PAA) as dispersant. The PAA addition effects on the SiC-Al2O3-ZrO2(3Y) mixture were investigated in terms of zeta potential, pH range for heterocharge region, dispersion of the mixed powders and rheology of the mixed slurry based on the study of each unary suspensions. The results show that before surface modification the SiC-Al2O3-ZrO2(3Y) mixed powders were agglomerated severely because they were in the heterocharge region with a broad pH range from 3.5 to 8.25, while after surface modification (pH = 10.5, PAA = 0.8wt%) the heterocharge region was narrowed with a relatively narrower pH range from 2.6 to 3.7. The mixed powders with homocharges were dispersed well because of the great electrostatic repulsive force and steric hindrance offered by PAA and the mixed suspensions had favorable rheology.