Diabetes is one of the most common comorbidities in adult patients with coronavirus disease 2019 (COVID-19). This study aimed to analyze the mortality risk factors of diabetic patients with COVID-19. A total of 167 patients with severe COVID-19, including 55 diabetic patients and 112 nondiabetic patients at Tongji Hospital, Wuhan, China from January 28, 2020, to March 10, 2020, were collected. The laboratory, radiological, management information, and medical history was retrospectively reviewed. Potential mortality risk factors in diabetic patients with COVID-19 were evaluated by the proportional hazard Cox model. The clinical information of 167 patients with severe COVID-19 was analyzed. The median age was 65.0 years. Approximately 32.9% of patients had diabetes. In total patients, older age, diabetes, and lymphocyte count were associated with increased risk of death. In diabetic patients, increased mortality was associated with decreased lymphocyte count (≤0.45×10⁹/L, HR 0.196, 95% CI 0.049-0.781, P = 0.021), lactate dehydrogenase >600 U/L (HR 8.010, 95% CI 1.540-41.670, P = 0.013), hsCRP >90 mg/L (HR 4.551, 95% CI 1.472-14.070, P = 0.009) and interleukin-10 >10 U/mL (HR 5.362, 95% CI 1.239-23.199, P = 0.025). COVID-19 patients with diabetes had a poor prognosis, especially when they had two or more of the following abnormalities (χ2 = 58.62, P<0.001): lymphocyte count was ≤0.45×10⁹/L, lactate dehydrogenase was >600 U/L, hsCRP was >90 mg/L and IL-10 was >10 U/mL. For diabetic patients with COVID-19, more attention should be paid to the dynamic monitoring of cytokine levels, and the control of hyperglycemia.