Abstract: The mechanism and potential energy surface of the hetero-Diels-Alder reactions of 9-silaanthracene or 9germaanthracene with alkenes were investigated using density functional theory (DFT) at the B3LYP/6311G^** level and the influences of some substituents on the potential energy surface were explored. The obtained results were compared with those of the corresponding reactions of silabenzene or germabenzene. The results show that all reactions occur in a concerted but nonsynchronous way and the formation of Si(Ge)—C bond always keeps ahead the formation of C—C bond. The phenyl group at C atom of ethylene molecules is not in favor of the heteroDielsAlder reactions thermodynamically, however, its influence on the kinetic properties of the reaction are determined by the relative position of phenyl with Si(Ge) atom in products. The mesityl substituent at Si (Ge) atom of 9silaanthracene or 9germaanthracene molecules has an unfavorable effect on the reactions both thermodynamically and kinetically.