The invention provides a process for preparing reeds or amur silvergrass activated carbon, which comprises steps of (1) cutting the reeds or amur silvergrass into segments, then drying, (2) employing one of the following methods to perform preprocessing, wherein one method is that the reeds or the amur silvergrass is completely impregnated in acetic acid solution formulated by acetic acid of 36% and water for 8 hours or 6 hours at normal temperature and then is sucked and filtered out, and the other method is that the reeds or amur silvergrass is impregnated in phosphoric acid solution to rest at normal temperature for 8 hours or 6 hours, (3) placing the preprocessed reeds or amur silvergrass in a muffle furnace or a carbonization furnace for performing carbonization and activation, taking out after being cooled in the furnace, then washing by distilled water to pH value of 6.5-7.0 and drying to finish. The invention employs the chemical method to prepare the reeds or amur silvergrassactivated carbon, the process is simple in procedure, high in efficiency and low in cost, and belongs to waste utilization and benefits environmental protection, and the reeds or amur silvergrass activated carbon with large specific surface area and high adsorption capacity can be obtained.