The invention provides a method for preparing active carbon by using urine to activate municipal sludge. The method comprises the following steps: mixing urine with dry sludge in a municipal sewage plant; carrying out centrifuging separation and drying on the mixed sludge, and carrying out carbonization on an obtained municipal sewage former body in a tube furnace in a nitrogen protection environment; after the carbonization is finished, controlling the temperature of the carbonized sludge obtained by naturally cooling to room temperature in a water steam protection environment for activation; after the activation is finished, naturally cooling to room temperature, then washing with a diluted hydrochloric acid water solution and deionized water in sequence until the pH value of the eluate is constant to be 6.7 to 7.0, and carrying out vacuum drying to obtain the active carbon. The preparation method provided by the invention has the characteristics of simple operation, easily obtained raw materials, low production cost and the like, and the obtained active carbon is high in specific surface area, developed in bore diameter and stable in product quality.