A high-resolution mass spectrometer combined with multiple data processing methods and various databases were employed to determine the components of flowers of Hemerocallis citrina Baroni (HF), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) pre-column derivatization combined with UHPLC–Q-TOF-MS method was used to screen antioxidant active compounds. A total of 132 components, including flavonoids, phenylpropanoids, lipids, alkaloids, and other types of compounds were identified. Among them, 41 chemical constituents were identified for the first time in HF. Eighteen compounds were screened with significant DPPH free radical scavenging activity. A sensitive UHPLC–QQQ-MS/MS method was first developed and fully validated for the simultaneous quantification of six phenylpropanoids and ten flavonoids in HF. The highest concentration of phenylpropanoids in HF was found to be 3-O-(E)-p-coumaroylquinic acid. In terms of flavonoids, rutin accounted for the highest concentration in HF. Correlation analysis was used to analyze the correlation between the contents of different compounds in different batches, Hierarchical cluster analysis (HCA) and principal component analysis (PCA) was used to distinguish HF of different origins. Considering the compounds content in HF, correlation analysis, principal component analysis and DPPH free radical scavenging activity, five components were recommended for the quality control of HF. •132 chemical components were identified in flowers of Hemerocallis citrina Baroni (HF).•41 compounds were identified in HF for the first time.•A method for determination of 16 compounds in HF was established.•DPPH pre-column derivatization with UHPLC-Q-TOF-MS identified antioxidant components.