Abstract: The alkylation of methylnaphthalene and methanol was carried out on HZSM-5 zeolite catalyst. The characteristics of coke deposited on the catalysts under the atmospheric pressure or supercritical fluid condition were found out and coke-burning reaction apparent activation energies of the used catalysts were calculated by using the thermo gravimetric analysis technique. The results showed that compared to the catalyst used at the atmospheric pressure, coke deposition was greatly depressed and life of catalysts increased 10 times under the supercritical fluid reaction condition. The coke-burning reaction of the used catalysts mainly happened at temperature range of 420 ℃ to 580 ℃. The longer reaction time led to higher peak temperature of weight loss and to greater coke-burning reaction apparent activationenergies of the used catalysts.