The invention relates to a device for continuously preparing activated carbon and a method for preparing the activated carbon by utilizing the device. The device for continuously preparing the activated carbon comprises an activation reactor. The device is characterized in that the activation reactor is a vertically arranged tubular reactor; the activation reactor is divided into a preheating section, a low-temperature activation section, a middle-temperature activation section, a high-temperature activation section and a cooling section from the top to the bottom along the axial direction. By utilizing the device for preparing the activated carbon, the prepared activated carbon is high in yield, large in surface area, high in porosity and wide in pore size distribution. The activation reactor is subjected to sectional control, and parameters (specific surface area, pore size distribution and pore volume) of a product can be conveniently controlled by controlling the working conditions of different sections.