Objective To investigate the significance of diameter measurement in descending aorta and ascending aorta as predictors of Stanford B type aortic dissection.Methods A total of 156 patients with chest pain and 100 healthy volunteers as control were enrolled in this study.The descending aorta diameter (dDA) and ascending aorta diameter (dAA) were measured by computed tomography (CT) and CT angiography(CTA),and the ratio of dDA to dAA or to rDA(radius of descending aorta) was calculated.Various metrics were analyzed for their specificity and sensitivity as screening measurements for Stanford B type aortic dissection.Results Fifty-six cases were diagnosed with Stanford B type aortic dissection by CTA with significant increases in dDA and rDA compared with control group(P＜0.05).When dDA was ≥ 30 mm,the sensitivity was 94.6％ and specificity was 82.0％ for Stanford B type aortic dissection,and when the rDA was ≥ 0.8,sensitivity and specificity were 96.4％ and 91.0％,respectively.Conclusions The dDA ≥ 30 mm and rDA ≥ 0.8 may be used to predict Stanford B type aortic dissection in suspected patients with chest pain,and the latter is more accurate than the former.