Abstract: Mesoporous activated carbon was prepared from poplar lignin by phosphoric acid activation. The effects of activation temperature(400-900 ℃) and mass ratio of phosphoric acid and lignin(impregnation ratio, 1∶1-4∶1) on the structure of activated carbon LAC-x-y(x represented the impregnation ratio, y represented the activation temperature) were investigated by pore structure, XRD and Raman spectroscopy analysis. The relationship between the electrochemical performance of activated carbon and its structure was investigated by means of electrochemical characterization. Pore structure analysis results showed that increasing the temperature and impregnation ratio was beneficial to the formation of mesopore, but too high temperature would lead to the collapse of pore structure, and too high impregnation ratio would lead to the increase of ash content, which would lead to the degradation of the performance of activated carbon. XRD and Raman spectroscopy results showed that increasing the temperature could improve the degree of graphitization of activated carbon, while increasing the impregnation ratio could decrease the degree of graphitization. Under the activation temperature of 800 ℃ and impregnation ratio of 2∶1, the activated carbon LAC-2-800 had the best performance, with specific surface area of 1 031 m²/g, mesopore ratio of 61% and average pore size of 3.31 nm. As the electrode material of supercapacitor, the specific capacitance reached 165 F/g at 1 A/g current density, and 136 F/g at 10 A/g current density. After 5 000 cycles at 1 A/g current density, the specific capacitance value could keep at 78.1% of the initial value.