The synergy of plasma and catalytic materials for CO₂ methanation provides the possibility for CO₂ reuse. The preparation method of catalytic materials plays an important role on their structure and performance. In this work, Ru/γ-Al₂O₃-P and Ru/γ-Al₂O₃-T catalytic materials were prepared by atmospheric-pressure H₂ plasma reduction and H₂ thermal reduction, respectively, using Ru/γ-Al₂O₃ precursor prepared by incipient wetness impregnation. The catalytic activity of Ru/γ-Al₂O₃ prepared by different methods was evaluated during atmospheric-pressure plasma reduction for CO₂ methanation reaction. Different techniques were used to investigate the effect of preparation methods on the structure of Ru/γ-Al₂O₃, analyze the influences of structural factor on the catalytic activity of Ru/γ-Al₂O₃, and discuss the preparation mechanism of Ru/γ-Al₂O₃-P and Ru/γ-Al₂O₃-T. The results show that the CO₂ conversion of γ-Al₂O₃ support is 24.8% under the combination of atmospheric-pressure plasma, and the main product is CO. However, the main CO₂ catalytic product of Ru/γ-Al₂O₃ is methane under the combination of atmospheric-pressure plasma. CO₂ conversion over Ru/γ-Al₂O₃-P is 77.3%, which is higher than that over Ru/γ-Al₂O₃-T (69.9%). Higher catalytic activity of Ru/γ-Al₂O₃-P is ascribed to the higher metallic Ru ratio and Ru/Al atomic ratio, as well as the smaller and higher dispersion of Ru nanoparticles. This work proves that highly active supported metal catalytic materials can be prepared by atmospheric-pressure H₂ plasma.