This study aims to explore the effect of baicalin (BAI) on renal fibrosis and renal injury in diabetic nephropathy by inhibiting the hypoxia inducible factor-1α (HIF-1α) / vascular endothelial growth factor (VEGF) / transforming growth factor-β1 (TGF-β1) pathway. The in vivo model of diabetic kidney disease (DKD) in rats was established by intraperitoneal injection of streptozotocin, and they were randomly divided into the control group, the negative control group (BAI, 200 mg/kg), the DKD model group, and the BAI low-dose group (50 mg/kg), BAI high-dose group (200 mg/kg). Serum and urine were collected to detect fasting blood glucose (FBG), serum creatinine (Scr), blood urea nitrogen (BUN), and 24-hour urine protein content. HE and Masson staining were used to evaluate renal pathology and fibrotic changes. Furthermore, a high glucose (HG) model of DKD was established in vitro using glucose-induced human renal tubular epithelial cells (HK-2), which were divided into the control group, HG model group, BAI treatment group, HIF-1α inhibitor group, and BAI + HIF-1α inhibitor group. The expressions of HIF-1α and TGF-β1 in kidney and HK-2 cells were detected by immunofluorescence and immunohistochemistry. The apoptosis of HK-2 cells was detected by TUNEL staining. The expressions of HIF-1α, VEGF, TGF-β1, SMAD family member 3 (SMAD3) , phosphorylated SMAD3 (p-SMAD3), matrix metalloprotein 9 (MMP-9), tissue inhibitor of metalloproteinase 1 (TIMP-1) and BCL-2 associated X protein (BAX), B-cell lymphoma-2 (BCL-2), cysteine aspartate-specific protease 3 (Caspase-3) proteins were detected by Western blot. Both in vivo and in vitro results demonstrated that BAI could significantly reduce FBG, Scr, BUN, and 24-hour urine protein content (P<0.05), protect against glomerular volume enlargement and tubular edema, and improve renal function. It also significantly inhibited the expression of HIF-1α, VEGF, TGF-β1, p-SMAD3/SMAD3, and MMP-9 in renal tissue and HK-2 cells，while promoting the expression of TIMP-1 protein (P<0.05). BAI can inhibit the HIF-1α/VEGF/TGF-β1 pathway, reduce extracellular matrix deposition, improve fibrotic damage, significantly decrease BAX and Cleaved-Caspase-3/Caspase-3 expression, increase BCL-2 protein expression (P<0.05), and inhibit apoptosis. The above results indicate that BAI has good hypoglycemic and renal protective effects. By down-regulating the expression of HIF-1α and inhibiting the HIF-1α/VEGF/TGF-β1 pathway, it alleviates renal fibrosis and renal injury in DKD.