Objective To investigate the kidney damage of the patients who have different severity of diabetic foot (Wagner grades 1 to 5) and investigate the relationship of diabetic foot with kidney disease in order to improve the clinical practice for diagnosis and treatment for diabetic foot. Methods A retrospective study was carried out on 622 type 2 diabetes mellitus (T2DM) patients with diabetic foot and 215 T2DM patients of non-foot disease admitted to the Department of Endocrinology of Chinese PLA Hospital No.306 from June 2009 to June 2014. Their clinical data were collected and biochemical indicators were measured. The patients with non-foot disease or Wagner grades l to 3 were assigned into a group, and those with Wagner grades 4 to 5 into another group. Urinary albumin/creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) were used to evaluate the kidney damage. The relationship of the renal function with varying degrees of diabetic foot was analyzed by SPSS19.0 software. Results The diabetic foot group had significantly higher UACR (78.00 vs 10.60mg/g, P＜0.05), but lower eGFR [(100.91±44.98) vs (114.27±35.88)ml/min·1.73m2, P＜0.05] when compared with the non-foot group. Multivariate stepwise regression analysis indicated that gender, diabetic retinopathy, serum albumin, uric acid, 2-hour postprandial plasma glucose (2hPPG), UACR were associated with the incidence and development of type 2 diabetic foot (β＝0.707, 0.850, -0.183, -0.006, 0.104, 0.003, all P＜0.05). The incidence of microalbuminuria (UACR 30?300mg/g) were significantly higher in the patients with Wagner grade 3 than those with grade 2 [49.7% (87/175) vs 39.2% (67/171), χ2＝3.885]. The ratio of renal insufficiency [eGFR＜60ml/(min·1.73m2)] was obviously higher in those with Wagner grades 4?5 compared with those with grade 3 [23.5% (43/183) vs 11.0% (24/220), χ2＝11.421, all P＜0.05]. Those with Wagner grade 3 had less incidences of macroalbuminuria (UACR≥300mg/g) and renal insufficiency than those with grade 2, but the incidences were increased again in those with Wagner grades 4?5. Conclusion The higher the Wagner classification grade is for diabetic foot, the more severe the kidney damage is. Microalbuminuria is superior to GFR to suggest kidney damage in diabetic patients. Wagner grade 3 is a turning point of the deterioration of kidney damage and clinical treatment. Clinicians should strengthen foot care and kidney protection when the patient is in Wagner grade 3.