Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS/MS) was employed to rapidly analyze and identify the chemical constituents of Selaginellae Herba.An Agilent Poroshell 120 SB-Aq (2.7 μm,2.1 mm×100 mm) chromatographic column was used with acetonitrile-0.1% formic acid aqueous solution as the mobile phase in gradient elution,at a flow rate of 0.4 mL/min and an injection volume of 3 μL.The electrospray ion source was selected to scan analyze in both positive and negative ion modes.The main chromatographic peaks of the obtained constituents were identified through retention time,accurate relative molecular mass,and secondary mass spectrometry fragmentation.A total of 54 compounds were identified in Selaginellae Herba,including 15 biflavonoids and flavonoids,12 selaginellins,ten phenolic acids,five benzenepropanoids,two steroids,two terpenoids,two amino acids and peptides,two esters,and four other categories.The UPLC-QTOF-MS/MS method established in this study can rapidly,accurately,and comprehensively analyze and identify the chemical constituents in Selaginellae Herba,providing a scientific basis for its quality control and pharmacological substance basis research.