Mume Flos is the dried flower bud of Prunus mume (Sieb.) Sieb.et Zucc.in the Rosaceae family,and the Prunus mume “Lve” is the main species used in clinical medicine.In this study,the chemical composition of Mume Flos was determined by ultra-high performance liquid chromatography with quadrupole electrostatic field orbitrap mass spectrometry (UPLC-QE-MS) at different developmental periods.A total of 328 compounds were detected,including 67 flavonoids,50 phenylpropanoids,104 terpenoids,26 phenols,24 alkaloids,11 organic acids and their derivatives,8 amino acid derivatives and 38 others.The semi-quantitative results showed a gradual decrease in the content of the main chemical constituents in Mume Flos with the developmental period.The content of the total flavonoid and phenylpropanoid was determined by UV-Vis spectrophotometry in Mume Flos samples at different developmental periods.The content of eight indicator components (neochlorogenic acid,chlorogenic acid,caffeic acid,rutin,hyperoside,isoquercitrin,isochlorogenic acid B and quercitrin) at different developmental periods was determined by UPLC,the results of the analysis showed significant differences in the content of components between the bud period (HL) and the full-opening period (QK) and that chlorogenic acid could be used as a marker of differential quality between the different developmental periods.The results of the DPPH radical scavenging assay on the antioxidant activity of Mume Flos at different developmental periods showed that the antioxidant capacity was closely related to the content of its components and gradually decreased with the development of flowers.The results of this paper can provide analytical methods and data support for the dynamics of the chemical constituents and the determination of the optimum harvesting period of Mume Flos.