In this study, low-temperature plasma is used to improve the wettability of polyacrylonitrile (PAN)-based high modulus (HM) carbon fibers with epoxy resin. The effect of plasma treatment time and power is studied. The results indicate that a time of 30 s is long enough for improving wettability of fibers with epoxy resin and there is an optimum power for plasma modification under the given conditions. According to the different effect of plasma treatment at different powers, we take two steps to treat the HM carbon fiber. First, the fibers are treated at moderate power to roughen the surface and then treated at low power to introduce some oxygen-containing functional groups. The results indicate the method is more effective in improving the wettability of HM carbon fibers with resin.