An on-line large volume sample stacking with polarity switching (LVSS) method was proposed for simultaneously determining lignanoids and ginsenosides in MEEKC. The parameters including the pH value and concentration of buffer solution, SDS, organic modifier, oil phase, running voltage, and temperature as well as injection time, sample matrix, stacking voltage, and time influencing separation and stacking were systematically optimized. The method was verified by performing precision, accuracy, stability, and recovery. Its reliability was proved by separating and quantifying two lignanoids and three ginsenosides in Shengmai injectionSMI. The sensitivity of these compounds was improved by MEEKC-LVSS method for 6-11 times than conventional MEEKC. Thus, this developed on-line MEEKC-LVSS method was sensitive, practical, and reliable.