Objective To establish a 3D finite element model of cervicothoracic spinal segments C5-T2 based on CT images and test its validity and effectiveness. Methods By using the Mimics, Geomagic and Hypermesh software, the 3D model of cervicothoracic spinal segments C5-T2 was reconstructed, repaired and pre-processed. Moment of ±0.5, 1, 1.5, 2 N?m were applied on top of the model to simulate loads produced during the flexion and extension movement of human body. The range of motion (ROM) of the segments C5-T2 during flexion and extension was calculated by ANSYS, and the reliability of the model was verified by comparing the experimental results in the previous literature with the finite element analysis results obtained in this study. Results Under the moment of 1 N?m, the ROMs of C5-6, C6-7, C7-T1 and T1-2 during flexion were 4.30°,3.21°,1.66° and 1.41°, and those during extension were 3.47°, 2.86°, 0.96° and 0.92°, respectively. The maximum stress during flexion appeared on the front of the vertebral body, while that during extension appeared on the back of the vertebral body. The trends of ROM and stress distributions were consistent with results reported in the previous literature. Conclusions The 3D model established in this study is accurate and realistic, and conforms to biomechanical properties of the cervicothoracic spine. The simulation results can be further used to explore clinical pathology of the spine and provide theoretical references for evaluation on cervicothoracic spine surgery.