In order to improve the interface compatibility of HDPE/bamboo fiber composites, O₂ and N₂ plasma were used to treat the HDPE surface, the effects of plasma treatment power, time, and different flow rates on HDPE surface wettability were analyzed, the optimal process of plasma to improve HDPE surface wettability was determined, and a mathematical model between HDPE surface energy and the plasma treatment process was established. The effect of plasma treatment on the mechanical properties of HDPE/bamboo fiber composites was further studied, and the surface morphology and surface chemical structure of the materials before and after plasma treatment were analyzed. The results show that the surface wettability of HDPE can be significantly improved after O₂ and N₂ plasma treatment, which can further enhance the interface compatibility of HDPE/bamboo fiber composites and improve the impact and tensile strength of the composites (impact strength increased by 19.91% and 19.55% after O₂ and N₂ plasma treatment, respectively; tensile strength increased by 16.47% and 12.48%, respectively). The optimal process parameters for enhancing the interface compatibility of the two plasma composites are 1100 W, 13 s, and 1.75 L/min (O₂ plasma), and 1100 W, 13 s, 2.5 L/min (N₂ plasma); between the two, N₂ plasma has a better effect on the surface wettability of HDPE than O₂ plasma treatment.