Objective：To investigate the relationship between vitamin D level and renal prognosis in patients with IgA nephropathy (IgAN). Methods：The general clinical data and pathological findings of IgAN patients diagnosed by renal biopsy in the First Affiliated Hospital of Nanjing Medical University from January 2014 to March 2019 were collected and analyzed retrospectively. The participants were divided into 25-(OH)D deficiency group and 25-(OH)D non-deficiency group. The end-point event was defined as progression of renal function，a doubling of serum creatinine or the onset of end-stage kidney disease(ESRD). The differences of renal function progression between 25-(OH)D deficiency group and 25-(OH)D non-deficiency group in IgAN patients were compared by Kaplan -Meier survival curve. Cox regression method was used to analyze the influencing factors of poor renal prognosis. Results：A total of 646 IgAN patients were enrolled in this study，there were 485 cases in 25-(OH)D deficiency group(75.08%)and 161 cases in 25-(OH)D non -deficiency group(24.92%). Compared with the 25-(OH)D non -deficiency group，the levels of hemoglobin，serum albumin，blood IgA and blood IgG were lower，and the levels of total cholesterol and urinary protein were higher in the 25-(OH)D deficiency group. The results of Kaplan-Meier survival curve analysis showed that the progressive rate of renal function in the 25(- OH)D deficiency group was higher than that in the non-deficiency group(log-rank test χ2 =4.217，P=0.040). The results of multivariate Cox regression analysis showed that 25-(OH)D deficiency was an independent factor affecting poor renal prognosis(HR=0.976，95%CI： 0.958~0.995，P=0.014). Conclusion：High level of 25-(OH)D has independent protective effect on renal prognosis in patients with IgAN. It implies that patients with low 25(- OH)D need supplementation of vitamin D.