Abstract: Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants that pose significant risk to human health and the environment. In this study, a plasma-assisted 5wt% (weight percent) MnO₂/γ-Al₂O₃ catalyst was employed for the efficient degradation of gas-phase naphthalene. The investigation focused, not only on degradation efficiency and mineralization degree of naphthalene but also on the control of intermediate products. The influence of catalyst loading on naphthalene conversion and carbon balance was first evaluated, and the 5wt% MnO₂/γ-Al₂O₃ catalyst exhibited superior performance across various discharge voltages. Based on this optimal loading, the variation patterns of intermediate products were further analyzed from the perspective of carbon balance. Subsequently, Response Surface Methodology (RSM) was used to optimize the reaction parameters for controlling intermediate species. Under the optimized conditions (24 kV discharge voltage and a 500 mL/min gas flow rate), the 7 h continuous discharge catalytic durability test showed stable catalytic activity, over 90.0% CO_x selectivity. Finally, the composition and changes of the intermediate products were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The results showed that while the types of intermediate products remained similar under different conditions, their concentrations were minimized under the optimized parameters. With prolonged reaction time, however, accumulated intermediate products tended to polymerize, forming higher molecular weight and higher boiling point compounds, such as 4,6-dimethyldodecane. This work provides valuable insights into the plasma-assisted catalytic degradation of PAHs and offers guidance for controlling intermediate byproducts in plasma-based environmental remediation processes.