Objective To analyze the differences in sagittal spino-pelvic parameters among adolescent idiopathic scoliosis (AIS) patients who underwent posterior spinal osteotomy orthopedic implant fusion and internal fixation with different distal fixed vertebrae.Methods The general data and imaging parameters of 49 AIS patients who underwent posterior spinal osteotomy orthopedic implant fusion and internal fixation in our hospital between Jan. 2010, and Nov. 2019 were analyzed retrospectively. The imaging parameters were measured preoperatively and at the last follow-up (at least 24 months after operation), including thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and the Cobb angles of proximal thoracic curve, main thoracic curve and thoracolumbar/lumbar curve, and PI－LL was calculated. According to the distal fixed vertebrae, the patients were divided into T₁₂-L₂ group and L₃-L₅ group. The general data and imaging parameters were compared between the 2 groups.Results There were 31 AIS patients in the T₁₂-L₂ group and 18 AIS patients in the L₃-L₅ group. There were no significant differences in age, gender, follow-up duration, Risser sign, or number of fused vertebrae between the 2 groups (all P > 0.05). There were no significant differences in SVA, PI, PT, SS, TK, LL, or PI－LL between the 2 groups before operation (all P > 0.05). Compared with those before operation, at the last follow-up, the LL was significantly increased in the L₃-L₅ group (P＝0.001) while significantly decreased in the T₁₂-L₂ group (P＝0.027), and the PI－LL was significantly increased in the T₁₂-L₂ and L₃-L₅ groups (1.8°[－4.0°, 8.7°] vs 0.3°[－4.7°, 5.7°]and －10.1°[－14.4°, －8.8°] vs 1.7°[－7.3°, 5.6°], P＝0.016 and 0.002). At the last follow-up, the change of PI－LL in the L₃-L₅ group was significantly greater than that in the T₁₂-L₂ group (P < 0.001).Conclusion For AIS patients, postoperative LL may increase when distal fixation is at L₃-L₅ during posterior spinal osteotomy orthopedic implant fusion and internal fixation, resulting in the mismatch between PI and LL, which may affect the sagittal spino-pelvic balance. The appropriate LL should be predicted according to PI before operation to avoid excessive bending of the rod during operation.