Objective To study pedicle screw internal fixation for thoracolumbar fracture, and to analyze the mobility and stress of each internal fixation model in different motion states by finite element method. Methods The data of a typical thoracolumbar fracture patient treated in our hospital in February 2018 were retrospectively analyzed. Spiral CT scanner was used to scan the T8-L4 segments of the spine, and a finite element model was established to simulate the posterior internal fixation operation. The mobility and stress of each internal fixation mode in different motion states were analyzed. Results (1) The activity of the double injury group with 6 nails was the smallest in different motion states, so it had the best biomechanical stability; the second was the right injury group; and the double injury group with 4 nails had the greatest activity in different motion states, so it had the worst biomechanical stability. (2) There was a significant difference in the stress of the upper screw in five groups of internal fixation models in different motion states (P < 0.05). In the forward bending state, the stress is the largest, so it has the best biomechanical tolerance; secondly, the left and right axis rotation; and the right-side bending has the lowest stress, so it has the worst biomechanical tolerance. (3) The stress ratios of upper and lower screw of five groups of internal fixation models in different motion states were significantly different, with statistical significance (P < 0.05). The stress ratio of upper screw and lower screw is the largest in the backward extension state, followed by right lateral bending and right axial rotation, while the stress ratio of upper screw and lower screw is the smallest in the left lateral bending state. Conclusion Finite element analysis in pedicle screw internal fixation for thoracolumbar fracture can fully study the activity and stress state of each internal fixation method in different motion states, which is helpful to determine the suitable internal fixation scheme for clinical use, and can effectively carry out early treatment and guide the rehabilitation of patients. It has a high application price. Value.