Surface modification of HDPE powders by oxygen plasma has been carried out in a circulating fluidized bed (CFB) reactor. The effects of solid holdup, treatment time and radio frequency (rf) power of oxygen plasma on the surface composition and hydrophilicity of HDPE powders have been determined. The solid holdup in the plasma reaction zone mainly governs the stability of plasma glow and surface property of the powders. The hydrophobic surface can be transformed to hydrophilic of HDPE powder and the oxygen functionalities. are formed including C double bondO and C(O)O-, which reach 12% and 8% respectively of the total carbon elements by the oxygen plasma treatment, The CFB reactor outperforms 3.4 times to obtain the similar level of hydrophilicity compared to that in a bubbling fluidized bed based on the composite parameter [(W/FM)t]. The present CFB reactor can be utilized to modify the polymeric surface from hydrophobic to hydrophilic with high-energy efficiency.