To analyze and identify the chemical constituents from the active part of Herba Cynomorii using UPLC/LTQ-Orbitrapa MS (Ultra Performance Liquid Chromatography/Liner Ion Trap-Orbitrapa Mass Spectrometry).Methods:The analysis was performed on an Acquity UPLC BEH C18 reverse phase column (100 mm × 2.1 mm，1.7 μm).The injection volume was 5 μL.The flow rate was 0.3 mL/min gradient elution and column temperature was 30 ℃.The mobile phase consisted of acetonitrile (B) and 0.1% formic acid (A) was used as gradient elute.MS conditions were ESI (Electronic Spray Ion)，positive and negative ion mode scanning.Results:After the data of mass spectra，pyrolysis rule and characteristic fragment ion information were analyzed，a total of 20 compounds were identified，including nucleosides，phenolic acids，flavonoid glycosides，Coumarins and amino acid.Conclusion:By using UPLC/LTQ-Orbitrapa MS method，the main chemical constituents from Herba Cynomorii can be accurately identified.