Abstract: Modification of activated carbon could increase the content of surface acid functional groups and NH3 adsorption capacity, which would strengthen adsorption refrigeration process using activated carbon-NH3 working pairs. Modification reagents were screened out. The effects of modification conditions on the content of superficial groups were investigated. Superficial microstructure of modified activated carbon was analyzed by FT-IR and SEM. Adsorption capacity of NH3 on activated carbon was measured. The results show that nitric acid modification can obviously increase surface acid functional groups of activated carbon. The feasible modification conditions are: concentration of nitric acid 4 mol/L, temperature 20℃, modification time 12 h. Compared to the original sample, the acidic functional groups content of activated carbon increased 3.5 times, adsorption capacity for NH3 increased 36.98% while iodine value decreased 9.20% after nitric acid modification.