The use of ionic liquid to catalyze the alkylation of isobutane and 2⁃butene has become a hot topic in recent years. The investigation on the formation mechanism of chlorinated hydrocarbons during the production process of alkylated oil catalyzed by ionic liquid is of great significance to improve the clean and environmental performance of gasoline. A set of independent reactions of chlorinated hydrocarbon formation system were determined by atomic coefficient matrix method. The Gibbs free energy change and equilibrium constant of each independent reaction in different reacting conditions were calculated by thermodynamics analysis method, which can be used to evaluate the occurrence possibility of the specified independent reaction in the given reacting conditions, and the results can be used to insight the formation mechanism of chlorinated hydrocarbons during the production process of alkylated oil catalyzed by ionic liquid.