Abstract: Panaxnotoginseng (Burk.) F.H. Chen or Sanqi in Chinese is a well-known Chinese medicinal herb, which has been used for thousands of years in China due to its good hemostatic effect. The major bioactive compounds of Panaxnotoginseng are Dammarane triterpenesaponins, especially protopanaxadiol and protopanaxatriol glycosides. While, the normal method of compounds identification in plants mainly based on the NMR spectra of the pure compounds, which obtained by isolation and purification on a scale of crude drugs. Liquid chromatography coupled with mass spectrometry (LC/MS) can identify and characterize the compounds, and has been increasingly developed for the compounds research of crude drugs. In this study, 17 compounds (notoginsenoside R₁, R₂, ginsenoside Rg₁, Rg₂, Rg₃, Rb₁, Rb₂, Rb₃, Re, Rf, Rc, Ro, Rd, Rk₁, Rh₁ and pseudoginsenoside F₁₁) in Panaxnotoginseng including four pairs of ginsenoside isomers were detected using ultra perform liquid chromatogram-electrospray ionization-quadrupole/time-of-flight mass spectrometer (UPLC-Q-TOF MS). Compounds were analyzed on Acquity UPLC^TM BEH C18 (2.1 mm×150 mm×1.7 μm) with acetonitrile (A) 0.1% formic acid aqueous solution (B) as mobile phase for gradient elution. The data were collected by negative electrospray ion mode using Q-TOF MS. The parameters of ion source were as follows: capillary voltage of 2 500 V, cracking voltage of 60-70 V, ion source temperature of 300 ℃, dry nitrogen flow rate of 800 L/h. Under this condition, all of 17 saponins were separated neatly within 1 h. The fragmentation behaviors especially the MS fragmentation rules of isomers were compared. According to the structure and the typical fragmentations, these saponins were divided into different typical types, and each type has its special fragments that can be easily identified. Meanwhile, the identification and structure of the 17 ginsenoside could provide essential and important data for the further studies on the multiple constitutions of Panaxnotoginseng as well as ginseng which also has the same or some similar constitutions. These findings are valuable for the identification of ginsenosides in plants especially Panaxnotoginseng.