The surface of HDPE polymer powder was fluorinated by CF₄ plasma in a fluidized bed reactor. Plasma is generated by an inductively coupled electrode at 13.56 MHz (rf) frequency, connected to an auto matching network and an rf power generator. In plasma surface fluorination, the CF₄ gas is diluted with He gas. The experimental variables are treatment time and rf power. The chemical property of the modified powder has been determined by using ESCA and FTIR. Plasma surface fluorination with the powder in a fluidized bed reactor results from the formation of CHF-CH₂, CHF-CHF and CF₂ groups. These fluorine functionalities and the fluorine atomic ratio on the surface increase with the treatment time and rf power. It has been found that the composite parameter is a good measure for determining the effect of total energy input on the plasma surface treatment of polymer powder in a fluidized bed reactor.