A novel concocting method to convert Triptolide (T) into Tripchlorolide (T4) in the traditional Chinese herb Tripterygium wilfordii Hook F. and a micellar electrokinetic capillary chromatographic (MEKC) approach by which the conversion of Triptolide (T) and Tripchlorolide(T4) was identified and determined had been established. Investigations of the influence of different pH values of boric acid and borax buffer and of sodium dodecyl sulfate (SDS) and organic additive concentrations had been carried out, and the optimum separation for T and T4 was achieved using boric acid and borax of pH 7.0 with 30mM SDS and 20% (volume ratio) methanol as the running buffer. It was found that MEKC exhibited good accuracy, precision and repeatability and the content of T4 was greatly increased in the herb that was treated by the new concocting method.