The columnar activated carbon from coal is modified by H2O2, and the specific surface area and oxygen containing functional groups of activated carbon are tested before and after H2O2 modified. The static adsorption capacity of trimethylamine, the dynamic penetration curve, and the desorption activation energy of activated carbon are also studied. Experimental results show that surface oxygen functional groups and specific surface area of activated carbon modified with oxidation are significantly improved, and activated carbon treated with 15% H2O2 for 1.5 h is the best. The trimethylamine adsorption capacity can reach 440.9 mg/g, which is 281.5% greater than before. The dynamic adsorption breakthrough time for trimethylamine increases from 10 min to 35 min, and the desorption activation energy increases from 11.461 kJ/mol to 15.663 kJ/mol, which proves that the adsorption performance of modified activated carbon is enhanced.