To rapidly analyze and identify the chemical composition of Chaxiong,one of the special Chinese medicine in Jiujiang area of Jiangxi Province,and its pharmacological substance basis is not clear,ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS /MS) was analyzed in this study.The chromatography was performed on a Titank C₁₈ column (100 mm×2.1 mm,1.8 μm) with acetonitrile -0.1% formic acid water as the mobile phase for gradient elution with a flow rate of 0.25 mL/min and an injection volume of 3 μL.The mass spectrometry was scanned in positive and negative ion modes with electrospray ion source (ESI) to identify the main chromatographic peaks of the obtained components by retention time,accurate relative molecular mass and secondary mass spectrometry cleavage fragmentation.The results of this study showed that a total of 72 chemical components were identified from Chaxiong,including 33 phenanthrene components,32 organic acid components,five alkaloid components,and two other components.The UPLC-Q-TOF-MS/MS method established in this study can quickly,accurately and comprehensively analyze and identify the chemical components in Chaxiong,providing a reference for its quality control and pharmacological substance basis research.