Type 2 diabetes mellitus (T2DM) causes osteoporosis by several mechanisms. Quantitative computed tomography (QCT) and Dual Energy X-ray absorptiometer (DXA) are commonly used to detect osteoporosis. For the diagnosis of osteoporosis in patients with T2DM, QCT is superior to DXA in mechanism. QCT can provide the measurement of bone microstructure and is not affected by the body size and bone size of subjects. Although DXA is vulnerable to the influence of body size and bone size of subjects and has certain defects, the results after adjusting BMI have certain credibility.