Abstract: Manual measurement of Cobb angle is the gold standard for the evaluation of scoliosis, however, there are some problems in locating end vertebrae and end lines. This paper proposed a computer-aided measurement, an improved Cobb angle measurement based on mask segmentation. The Cobb angles of 134 randomly selected digital X-ray images of patients with scoliosis were measured using traditional manual method, and the results were taken as the test standard. The improved measurement proposed by this study was used to measure the same images. Results show that the improved Cobb angle measurement method is consistent with that of the manual method. With the improved Cobb angle measurement, the problem of locating end vertebrae and end lines is solved, and the reliability and accuracy of measurement is improved.