OBJECTIVE：To estab lish a method that can comprehensively and rapidly analyze the chemical compositions of Miao medicine Caesalpinia decapetala，and to providing reference for quality control and pharmacodynamic material basis study of C. decapetala . METHODS ：UPLC-Q-TOF-MS/MS was adopted . The determination was performed on Agilent SB-C 18 column with mobile phase consisted of 0.1％ formic acid solution- 0.1％ formic acid acetonitrile （gradient elution ）at the flow rate of 0.25 mL/min. The column temperature was 30 ℃，and sample size was 2 µL. ESI source was applied in negative and positive scanning ion mode and data collection range of m/z 50-1 500. The capillary voltage was 4.5 kV，the atomizing gas （nitrogen）pressure was 1.2 Bar， the solvent removal gas was nitrogen ，the flow rate of solvent removal gas was 8 L/min and the solvent removal gas temperature was 200 ℃. Data Analysis 4.2 software was adopted to analyze fragment ion information of each peak ，and identify chemica l compositions on the basis of relevant literature and mass spectograms of reference substance. RESULTS ：Under positive ion mode ， 9 chemical compounds were identified ；peak 1，2，3，4，5，6，7，8，9 were catechin ，protohematoxylin B ，epicatechin，ethyl gallate，quercetin，luteolin，3-deoxy-hematoxylin chalcone ， isoliquiritigenin and linoleic acid. Under negative ion mode ， U1812403）， totally 21 peaks were confirmed and 13 compounds were identified；peak 3，4，5，6，7，8，9，10，11，12，13，15， 21 were catechins ， brevifolin carboxylic acid ， proto- hematoxylin B ，epicatechin，ethyl gallate ，epicatechin gallate ， quercetin，resveratrol，hematoxylin，luteolin，3-deoxy-hema- toxylin， isoliquiritigenin， linoleic acid. CONCLUSIONS UPLC-Q-TOF-MS/MS method is established successfully for analysis of chemical compositions in C. decapetala .