Objective To explore the safety and effectiveness of one-stage posterior eggshell osteotomy and long-segment pedicle screw fixation in the treatment of ankylosing spondylitis kyphosis combined with acute thoracolumbar vertebral fracture. Methods A clinical data of 20 patients with ankylosing spondylitis kyphosis combined with acute thoracolumbar spine fracture, who were treated with one-stage posterior eggshell osteotomy and long-segment pedicle screw fixation between April 2016 and January 2022, was retrospectively analyzed. Among them, 16 cases were male and 4 cases were female; their ages ranged from 32 to 68 years, with an average of 45.9 years. The causes of injury included 10 cases of sprain, 8 cases of fall, and 2 cases of falling from height. The time from injury to operation ranged from 1 to 12 days, with an average of 7.1 days. The injured segment was T11 in 2 cases, T12 in 2 cases, L1 in 6 cases, and L2 in 10 cases. X-ray film and CT showed that the patients had characteristic imaging manifestations of ankylosing spondylitis, and the fracture lines were involved in the anterior, middle, and posterior columns and accompanied by different degrees of kyphosis and vertebral compression; and MRI showed that 12 patients had different degrees of nerve injuries. The operation time, intraoperative bleeding, intra- and post-operative complications were recorded. The visual analogue scale (VAS) score and Oswestry disability index (ODI) were used to evaluate the low back pain and quality of life, and the American spinal cord injury association (ASIA) classification was used to evaluate the neurological function. X-ray films were taken, and local Cobb angle (LCA) and sagittal vertical axis (SVA) were measured to evaluate the correction of the kyphosis. Results All operations were successfully completed and the operation time ranged from 127 to 254 minutes (mean, 176.3 minutes). The amount of intraoperative bleeding ranged from 400 to 950 mL (mean, 722.5 mL). One case of dural sac tear occurred during operation, and no cerebrospinal fluid leakage occurred after repair, and the rest of the patients did not suffer from neurological and vascular injuries, cerebrospinal fluid leakage, and other related complications during operation. All incisions healed by first intention without infection or fat liquefaction. All patients were followed up 8-16 months (mean, 12.5 months). The VAS score, ODI, LCA, and SVA at 3 days after operation and last follow-up significantly improved when compared with those before operation (P<0.05), and the difference between 3 days after operation and last follow-up was not significant (P>0.05). The ASIA grading of neurological function at last follow-up also significantly improved when compared with that before operation (P<0.05), including 17 cases of grade E and 3 cases of grade D. At last follow-up, all bone grafts achieved bone fusion, and no complications such as loosening, breaking of internal fixation, and pseudoarthrosis occurred. Conclusion One-stage posterior eggshell osteotomy and long-segment pedicle screw fixation is an effective surgical procedure for ankylosing spondylitis kyphosis combined with acute thoracolumbar vertebral fracture. It can significantly relieve patients’ clinical symptoms and to some extent, alleviate the local kyphotic deformity.