In this article, the sludge-based activated carbon was prepared by the sewage sludge from the municipal wastewater treatment plants with ZnCl2 as the activator. The concentration of the activator was 30% and the pyrolysis temperature and duration were 500°C and 1 hour, respectively. The yield of sludge-based activated carbon was 30.14% with 4.66% ash. Under the best preparation condition, carbon content would be highest and the pore structure would be clear. The sludge-based activated carbon was mainly composed of mesopores. The main adsorption peaks of the sludge-based activated carbon were C-O-C (1078.3 cm-1), C=C（1568.7 cm-1）and –OH（3190.9 cm-1）groups.