Objective:To analyze and identify the flavonoids of Citri Reticulatae Pericarpium with different aging time by an ultra-performance liquid chromatography-quadrupole-electrostatic field orbitrap high resolution mass spectrometry （UPLC-Q-Orbitrap HRMS）. Method:Compounds were separated on Agilent Extend-C₁₈ column （3.0 mm×100 mm， 1.8 μm）， mobile phase was 0.1% acetic acid aqueous solution （A）-0.1% acetic acid methanol solution （B） for gradient elution （0-25 min， 5%-95%B； 25-30 min， 95%B； 30-30.1 min， 95%-5%B； 30.1-35 min， 5%B）， the flow rate was 0.4 mL·min^-1， and the column temperature was set at 30 ℃. High resolution mass spectrometry was performed with electrospray ionization （ESI）， and scanned in positive and negative ion modes by means of full scan/data dependent secondary scan （Full MS/dd-MS²）. The multistage ion fragment information combined with mzCloud network database， local high resolution mass spectrometry database of traditional Chinese medicine components （OTCML）， literature information and relevant reference materials were used for accurate qualitative analysis. Result:Totally 43 flavonoids in Citri Reticulatae Pericarpium were identified， including 24 flavones， 5 flavonols， 13 dihydroflavones and 1 chalcone. The flavonoids in samples with different aging time were basically consistent in material types， but the peak area was different. According to the comparison of relative content in the peak area， it was found that the relative contents of 30 flavonoids showed an overall increasing trend with the increase of aging time. Among them， the relative contents of 24 flavonoids （such as hesperidin， diosmin， 6-demethoxytangeretin， nobiletin and tangeretin） increased significantly. There was no significant change in the relative contents of the other 13 flavonoids （such as naringenin and neohesperidin）. Conclusion:An efficient method is established in this paper to identify flavonoids in Citri Reticulatae Pericarpium with different aging time and their relative content changes rapidly and accurately. The findings provide a methodological reference for the study on pharmacodynamic material base and quality control of Citri Reticulatae Pericarpium， and it provides experimental basis that drugs processed long time ago have better effect of Citri Reticulatae Pericarpium.