Abstract: In order to investigate the effect of substrate conductivity on the characteristics of atmospheric pressure micro-plasma jet, in the process of polymer film processing, we analyzed the plasma jet with three kinds of substrates, copper, silicon, and glass through experiments, generated by a ring-rod jet device. The characteristics of the discharge waveform under the three different substrate conditions were similar, but there were numerical differences in the root mean square value of current and the dissipated power, and the substrate with higher conductivity enhanced the discharge intensity of the plasma jet. The gas temperature and the electron temperature were calculated by optical emission spectra scanned in the range from 200 nm to 850 nm. Under three conditions, the gas temperature ranged from 310 to 365 K, and the electron temperature was 2118 K, 1958 K and 1380 K, separately. With copper substrate, the emission spectral intensity of the jet was the strongest and had the highest electron temperature, which could be considered to have more high-energy electrons and active species. The PET films were treated with the jets under three conditions for 15 s. The water contact angle decreased from the initial 78.1° to 22.2°, 26.3°, and 28.3°, respectively. It can be seen that the atmospheric pressure micro-plasma jet with the substrate of higher conductivity enhances processing efficiency. These results have important implications for the process of atmospheric pressure micro-plasma jet processing of polymer films.