Using Epimedium as research object, Lactobacillus plantarum as fermentation strain, the changes in the scavenging ability of 1,1-diphenyl-2- picrylhydrazyl radical (DPPH) and hydroxyl radical and the contents of polyphenols, total flavonoids and polysaccharides were studied during the Epimedium fermentation process, and the changes of main active components of Epimedium before and after sterilization and during fermentation process were analyzed by ultra high performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-Q-TOF-MS). After fermentation by L. plantarum, the scavenging rate of DPPH free radical and hydroxyl free radical, total flavonoids, polyphenols and polysaccharide contents of Epimedium were significantly increased, which were 29.59%, 46.33%, 11.90 mg/L, 1.51 mg/L and 0.18 g/L, respectively, when fermentation time was 37 h. A total of 57 active chemical constituents were identified by UPLC-Q-TOF-MS, including flavonoids 51, phenolic acids 4 and other compounds 2. After fermentation by L. plantarum, the relative contents of flavonoid aglycones, monoglycosides and phenolic acids in Epimedium increased, while the relative contents of flavonoid multilevel and secondary glycosides decreased.