The method and model for the separation of capsaicin-type alkaloids with ionic liquid(BmimBF4) as additives were established,and the separation mechanism was studied.The influence factors,including kind of ionic liquid,concentration of ionic liquid,length of alkyl groups in room temperature ionic liquids(RTILs) and column temperature were investigated.It was shown that the chromatographic behaviors of the analytes with a mobile phase containing ionic liquids of chaotropic anion were signally improved.The relationships between retention value and concentrations of different lengths of alkyl groups in ionic liquid preferably complied with the stoichiometric displacement model for retention(SDM-R),r＞0.99.It was clarified that the interactions between solutes and imidazole cations were almost completely competitive adsorption on the stationary phase.