Abstract: The alkylation of isobutane with butene catalyzed by Et₃NHCl-AlCl₃-CuCl ionic liquid was carried out in a continuous stirred autoclave reactor; deuterated isobutane was used as an isotope tracer to investigate the reaction mechanism of alkylation. The results indicate that the induction period of alkylation catalyzed by Cl-AlCl₃-CuCl is less than 30min. Tri-methyl-pentanes are primarily produced from the self-alkylation of isobutane, the alkylation of isobutane with 2-butene and the cracking of C₁₂⁺ intermediates, whereas the undesired di-methyl-hexane is mainly formed from the addition reaction between sec-C₄⁺ and 2-butene.