Abstract: Packed-bed reactors (PBRs) hold great promise for environmental applications, but a deeper understanding of the behavior of plasma discharge within PBRs is required. To this end, a partial-discharge alternative equivalent circuit for PBRs was established in this work. Dielectric particles (glass beads or glass sand) were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs. Some electrical characterizations were explored (e.g. the effective dielectric capacitance, partial discharge coefficient, and corrected burning voltage) that may differ from long-standing interpretations. The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size. For partial discharge, the effective dielectric capacitance is always less than the dielectric capacitance. The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size. As compared to an empty reactor, the average electric field in the PBR was found to be improved by 3–4 times, and the ozone energy efficiency and production were promoted by more than 20% and 15%, respectively. The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex, irregularly-shaped packing material that is suitable for the discharge gap.