Introduction Glucose tolerance is often impaired in pulmonary tuberculosis (TB) patients. We aimed to explore the relationship between computed tomography (CT) findings of TB and blood glucose levels in diabetes mellitus (DM) patients. Methods 763 diabetes mellitus patients with pulmonary tuberculosis (DMTB) from March 2015 to March 2018 were selected and their clinical data were retrospectively evaluated. CT appearance of DMTB was reviewed and compared according to blood glucose levels and CT scores. TB scores were calculated according to the combination of typical and atypical CT appearance. The relationship between blood glucose levels and CT scores was analyzed via Pearson correlation coefficient. Results TB lesions mainly occurred in the left lung and the lower lobes in the DMTB patients. Nodules and cavities are the main typical complications in these DMTB patients, and especially the number and size of cavities predominantly contribute to CT scan scores. The size of cavities (diameters (cm), median (95% CI of median)) was 0.72 (0.66–0.77), 1.20 (1.09–1.28), and 3.45 (2.92–3.94) from the low-, middle- and high-CT-score groups, respectively. The patients with high CT scores had a higher level of fasting plasma glucose (mean 13.48 mM, 95% CI of median 12.56–14.44 mM) than the patients in the low-CT-score (mean 8.73 mM, 95% CI of median 8.49–9.36 mM) and middle-CT-score groups (mean 10.16 mM, 95% CI of median 9.89–10.49 mM) (P < 0.0001). CT scores have a consistent relationship with the levels of blood glucose (rho = 0.60, P < 0.0001). Conclusions CT appearance stands for the severity of tuberculosis and is closely associated with blood glucose levels in diabetic TB patients.