Objective: To investigate the application value of serum 25-hydroxy vitamin D [25(OH)D] in systemic lupus erythematosus (SLE). Methods: Data of 158 patients with SLE in Department of Rheumatology and Immunology in the People’s Hospital of Xinjiang Uygur Autonomous Region from July 2016 to July 2019. All the SLE patients were divided into two groups by SLE scores of the disease activity index (SLEADI): 59 cases of active group (SLEADI>4), 99 cases of non-active group (SLEDAI ≤4). Fifty healthy people were selected as healthy control group. The patients’ general information and their laboratory data including serum 25(OH)D levels were collected. Statistical methods used were t-test, Spearman’s correalation analysis and Logistic regression analysis. Results: (1) A total of 208 cases were included in this study. The level of 25(OH)D in SLE group [10.4(5.6,15.8) μg/L] was significantly lower than that in healthy control group [25.5(22.8,32.3) μg/L, P<0.01]. 25(OH)D level in active SLE patients [6.2(3.7,13.8) μg/L] was significantly lower than that in remission SLE patients [12.3(7.2,16.7) μg/L, P<0.01]. The serum 25(OH)D level in lupus nephritis [6.7 (4.4, 12.9) μg/L] was significantly lower than that in SLE without renal involvement [13.3 (7.4, 18.7) μg/L, P<0.01]. (2) A significant negative correlation was demonstrated between the serum level of 25(OH)D and SLEDAI (r=-0.35,P<0.01), and the 24h urinary protein excretion (r=-0.39, P<0.01).Positive correlation was demonstrated between the serum level of 25(OH)D and C3 that decreased (r=0.249, P<0.05). (3) Univariate analysis showed anti- dsDNA antibodies(ds-DNA), anti-Sm antibodies(Sm), IgG, C3, C4, erythrocyte sedimentation rate (ESR), 24h urinary protein quantification(24h-pro) and 25(OH)D were associated with disease activity in the SLE patients; Multivariate Logistic regression analysis showed that 25(OH)D was associated with the disease activity of the lupus patients. Conclusion: The decrease of vitamin D level is related to the disease activity of SLE patients, and may be related to lupus nephritis, which plays an important role in the occurrence and development of SLE.