Deposition of nanoiamond thin films at low temperature using GPCVD(glow plasma chemical vapor deposition)technique and its mechanism have been studied in this paper. In order to lower the substrate temperature, a barrier pole has been employed between the hot filament and the substrate, which can change distribution of electric field, imitate and create an electric double layer. Moreover, the effect of the barrier on diamond deposition at low temperature has been studied. The films were grown on (100) silicon wafer, high pure H2 and high pure CH4 feed gases were used. The samples?morphology and structure properties have been analyzed by Scanning electronic microscopy (SEM), Xay diffraction (XRD)and Raman Spectra. Our work consists of two parts. When the barrier was not employed, highuality diamond films were synthesized at 3000C.