Activated carbon with reasonable pore structure used for electric double layer capacitor (EDLC) was prepared with tobacco stem as raw material and KOH as activator by chemical activation after carbonization at 500～800 ℃. The specific surface area and pore structure of activated carbon were characterized by nitrogen adsorption isotherm at 77 K. The pore volume and mesoporosity of activated carbons increased with decrease of carbonization temperature, while the BET surface area increased firstly and decreased afterwards. The electrochemical behaviors were characterized by means of galvanostatic charging/discharging, cycle voltammetry and impedance spectroscopy. The correlation between electrochemical properties and pore structure was investigated. The results show that TS-AC samples with high mesoporosity exhibited excellent high current charge/discharge performance of 80% capacitance maintenance when current density was enlarged 50 times. And TS-AC-600 exhibited the highest specific dc capacitance over 190 F•g^－1 at 1 mA•cm^－2, which possess the highest specific surface area and pore volume, 3333 m²•g^－1 and 2.47 cm³•g^－1, respectively.