A process is adopted to grow whiskers on carbon fibers. The whisker growth is carried out in a two-step process. Plasma spraying, electroplating and magnetron sputtering are used to pretreat the surface of carbon fibers and then ZnO whiskers are grown by hydrothermal method. By comparing three different methods of surface pretreatment, it is concluded that magnetron sputtering is most available and has no damage to the carbon fibers. Combining preparation method of the ZnO whiskers, a new process is developed to surface modified of carbon fibers which is expected apply to carbon fiber composites.