Abstract: The effects of torrefaction pretreatment on the preparation and properties of activated carbon by phosphoric acid using corn straw as the raw materials were studied. The results showed that the contents of carbon and fixed carbon were increased and the volatile content was reduced using torrefaction pretreatment which increased the quality of pyrolytic carbon. The effect of torrefaction temperature was stronger than that of torrefaction time. By torrefaction pretreatment, the specific surface area of activated carbon increased firstly and then decreased, the total pore volume and the mesoporosity decreased, while the microporosity increased significantly. The adsorption performance of activated carbon could be improved by torrefaction pretreatment. As 100 g corn straw with the particle size of 154-450 μm were pretreated under the torrefaction temperature of 240 ℃ and torrefaction time of 60 min, the pretreated corn straw contained carbon, fixed carbon, and ash with the mass fractions of 51.32%, 27.64% and 4.72%, respectively. The activated carbon was prepared from the pretreated corn straw under the impregnation ratio of 1∶4(i.e., the mass ratio of the pretreated corn straw and 55% phosphate acid), dipping temperature of 140 ℃, dipping time of 90 min, activated temperature of 400 ℃, activated time of 60 min, the specific surface area of the obtained activated carbon reached 1 317.05 m²/g, and the values of iodine adsorption, methylene blue adsorption, and caramel decolorization were 876 mg/g, 210 mg/g and 100%, respectively.