The active component polysaccharide of Osmunda japonica Thunb was extracted and its chemical structure was detected by FT-IR, 1D-NMR and 2D-NMR spectra, in order to have a positive preventive and therapeutic effect on uterine fibroids. The physicochemical properties of Osmunda japonica Thunb polysaccharides (OPP) were analyzed, and the results showed that OPP was heteropolysaccharides composed of six monosaccharides. Ara and Glc were the main monosaccharides of the polysaccharide, with a molecular weight of 252.54 ± 10.84 kDa. The main chain was connected by 1,3-linked Araf, which had a high degree of branching, and was connected to the branch at the O-2 and O-3 positions. The mice model of uterine fibroids was established by the estrogen load method. The coefficient of the uterus in the mice model increased significantly, irregular nodular processes were observed in the uterus, focal hyperplasia appeared in the smooth muscle layer, cell enlargement, disordered arrangement of smooth muscle cells, and endometrial hyperplasia was obvious. Furthermore, this work found that the serum estradiol (E2) and progesterone (P) concentrations in the model group were significantly higher than those in the normal group (P