Abstract: In this paper,studies were made of the yield and adsorption properties of the actived carbon and the process of preparing activated carbon by using agricultural waste straw and the water vapor activation method.Discussion was made on according to the carbonization temperature,carbonization time,activation temperature and activation time,thus obtaining the optimum process conditions:carbonization temperature of 450℃,6 hours of carbonization time,850℃ of activation temperature,and 3 hours of activation time.The methylene blue adsorption value of activated carbon was 180 mg·g^-1 after the ash content of postprocessing.The basic energy could reach the standard of activated carbon for water purification,and it had a great prospect of popularization and application.