A novel analytical method was developed for the separation of tropane alkaloids by high performance liquid chromatography(HPLC) using ionic liquid(OminPF6) as mobile phase additive.The retention model and mechanism for the ionic liquid were also illustrated.The effect factors,including wavelength of detection,type and proportion of organic phase,pH value,type and concentration of ionic liquid and buffer salt system on retention behavior of components were investigated.The results showed that,the ionic liquid as mobile phase additive could significantly improve the separation effect on tropane alkaloids,and also increase the symmetry of peak and the relative separation.The results also showed that the relationship between capacity factor and concentrations of ionic liquid preferably complied with the stoichiometric displacement model for retention(SDM-R)，and the retention process of alkaloids was mainly based on competitive adsorption function.