The structural parameters of electrostatic separators used for the fluid catalytic cracking slurry (FCCS) are critical factors affecting the separation efficiency. This study investigated the influence of the filler diameter, stacking manner of fillers and inner electrode diameter on the separation efficiency. Simulation studies were carried out with experimental data considering change in the stacking manner of fillers and filler diameter; the filler diameters were 1.5 mm, 3 mm, and 5 mm, and four stacking manners were considered, namely face centered cubic (fcc), body centered cubic (bcc), simple cubic (sc), and hexagonal close packing (hcp). Experimental investigation was carried out by conducting tests in which the diameter of the inner electrode was varied from 8 mm to 16 mm. The results showed that with increase in the filler diameter, the separation efficiency decreased. The stacking manner of fcc corresponded to the highest separation efficiency. Further, the separation efficiency first decreased and later increased with increase in the inner electrode diameter. In addition, both the average electric field strength and nonuniformity coefficient influenced the separation efficiency. These findings could assist in the optimization of the structure of electrostatic separators and predict the separation effect.