Background: Previous studies have demonstrated that type 2 diabetes mellitus (T2DM) is negatively correlated with the occurrence of aortic dissection (AD). This study aimed to investigate the effects of T2DM on the prognosis of Stanford type B AD (STBAD) patients after thoracic endovascular aortic repair (TEVAR). Methods: STBAD patients (n = 141) who underwent TEVAR received an oral glucose tolerance test (OGTT) and were divided into a normal glucose (NG, n = 55) group, an abnormal glucose tolerance (AGT, n = 48) group and a T2DM (n = 38) group according to the results of the OGTT. Data on mortality, clinical complications, left ventricular (LV) remodeling and aortic remodeling were collected during the 3-year follow-up. Results: Lower mortality and fewer clinical complications after TEVAR were found in the T2DM group than in the NG group. Multivariate linear regression analysis showed that 2-hour postprandial glucose (Glu-2h) was negatively correlated with mortality and the occurrence of clinical complications in STBAD patients after TEVAR. In addition, better LV remodeling, larger true lumen areas and smaller false lumen areas in both the proximal aortas and abdominal aortas were observed in the T2DM group than in the NG group. Furthermore, no significant differences in mortality or clinical complications after TEVAR were found between the NG group and the AGT group or between the T2DM group and the AGT group. Conclusion: During the 3-year follow-up period, mortality and clinical complications in STBAD patients after TEVAR were significantly reduced in the T2DM group. For STBAD patients who undergo TEVAR, properly relaxing of blood glucose control requirements may be beneficial for their prognosis.