Activated carbon was modified by hydrochloric acid and aqueous ammonia and used as adsorbent to remove methyl orange (MO) from wastewater. The effects of modification condition, shaking speed and temperature on its adsorption performance of MO were examined. The adsorption data were simulated by both adsorption isotherm and kinetic models, and the adsorption thermodynamics was also analyzed. The results showed that the adsorption capacity of hydrochloric acid modified activated carbon for MO was better than that of ammonia modified one. The adsorption equilibrium was achieved with the removal rate of MO 93.7% within 24 h under the conditions of initial MO concentration of 60 mg/L, solution volume of 50 mL, temperature of 20℃ and shaking speed of 100 r/min. The adsorption data of hydrochloric acid modified activated carbon for MO fitted well to Langmuir (RC2>0.95) and Freundlich (RC2>0.97) adsorption isotherm models, and its saturated adsorption capacity reached up to 112.7 mg/g. Thermodynamic parameters, such as DG0<0, and DH0>0, DS0>0, showed that the adsorption of MO on hydrochloric acid modified activated carbon was a spontaneous and endothermal reaction. The adsorption kinetics could be well described by pseudo-second-order kinetic model. The adsorption rate constant increased with the increase of shaking speed.