In this study, we developed a flat plate-type wet electrostatic precipitator that generates stable corona discharge compared to wire-type discharge electrodes. Particle removal efficiencies were compared among differing shapes of the discharge electrode, including varying horizontal and vertical distances between spiked edges, and varying the height of the discharge pin support. When the horizontal distance between spiked edges was increased to 36 mm, the vertical distance between spiked edges increased to 54 mm, and when the height of the discharge pin support was increased to 76 mm, the removal efficiency of PM10 was maintained at approximately 60.0%. Furthermore, the removal efficiency of particles over 5 μm was about 80% or greater. When the flow rate was 4 m s−1, the gap between collection plates was 60 mm, and −14 kV was applied to the discharge electrode. The particle removal efficiency of the flat plate-type electrostatic precipitator was maintained when the horizontal and vertical distances between spiked edges and the height of the discharge pin support were below threshold levels. Those variables may be important factors for designing the shape of the discharge electrode. Therefore, when designing electrostatic precipitators with multiple channels, the discharge electrode weight and processing costs must be considered when determining the optimal horizontal and vertical distances between spiked edges and the height of discharge pin support.