A method was established for identifying the chemical components of a traditional Chinese medicinal formula Baihe Zhimu Tang and its single herbs by combining high performance liquid chromatography and electrospray ionization mass spectrometry(HPLC-ESI-MS). The molecular ions of compounds in both negative and positive modes were observed for molecule mass information, and the potential structures were identified by attentive studying on the mass spectra of compounds and comparing with Reference data and some of standards. The results show that in MS detection, saponins in Baihe Zhimu Tang and its single herbs are easily to become positive ions in the electrospray ionization procedure, and they have strong responses, but the mass spectrometric signals of flavonoids and phenolic glucosides are week. 38 compounds in Baihe Zhimu Tang including 3 flavonoids, 4 phenolic glucosides and 31 saponins were identified through analyzing and comparing the total ion chromatograms(TIC) and mass spectra of Baihe Zhimu Tang and its single herbs. This method has the advantages of simple operation, rapid measurement and it is a powerful tool for identification of chemical components in Baihe Zhimu Tang.