Objective   To analyze the stress changes of thoracic vertebra (T)11-sacrum (S) titanium rods in patients with ankylosing spondylitis after vertebral column decancellation (VCD) osteotomy, and provide reference for the selection and improvement of titanium rods before surgery. Methods   The original data of the continuous scanning tomographic images of patients with ankylosing spondylitis after VCD osteotomy were imported into Mimics 21.0 in DICOM format, and T₁₁-S vertebrae, screws and titanium rods were respectively reconstructed. They were imported into 3-Matic to establish a preliminary geometric modeling, and then processed with noise removal, paving, smoothing, etc. The improved model was imported into Hypermesh 10 software for grid division, and the material was imported into ANSYS 19.2 to display the finite element model after attribute assignment, Set the boundary and load conditions, and measure the stress value at the connection between the screw and the titanium rod. Results Under neutral position, forward bending, lateral bending, and axial rotation conditions, the titanium rod had the highest stress at the upper vertebrae (T₁₁) and the lowest stress at the top vertebrae (L₃); Under the backward extension condition, the titanium rod has the highest stress at the lower end vertebra (L₅). Conclusion   In the upper and lower vertebrae, it is possible to consider increasing the diameter of the titanium rod, enhancing its hardness, or changing it to a double rod.