Objective To investigate the therapeutic effect of segmental decompression combined with corrective short-segment fusion surgery for the treatment of degenerative lumbar scoliosis. Methods In total, 124 patients with degenerative lumbar scoliosis were selected and divided into short- and long-segment fusion groups using the random number table method, with 62 patients in each group. Posterior short-segment decompression, fixation, and fusion were performed in the short-segment fusion group; the fusion segment was the adjacent lumbar vertebra. Posterior long-segment decompression, fixation, and fusion were performed in the long-segment fusion group; the fusion segments included multiple adjacent lumbar vertebrae. At the 6th month after surgery, the coronal Cobb angle of lumbar convexity, sagittal Cobb angle of lumbar lordosis, intervertebral foramen height, intervertebral space height, intervertebral foramen area, spinal canal area, spinal canal diameter, Japanese Orthopedic Association (JOA) score, Oswestry Disability Index (ODI), degree of pain in the lower back and lower limbs, and postoperative complications were compared between the groups. Results The Cobb angle of the coronal lumbar scoliosis in the short- and long-segment fusion groups was significantly higher than that before surgery (P < 0.05). At the 6th month after surgery, the intervertebral foramen height, intervertebral space height, intervertebral foramen area, spinal canal area, and spinal canal diameter in both groups increased, and those in the short-segment fusion group were higher than those in the long-segment fusion group (P < 0.05); at the 6th month after the operation, the JOA scores of the short-segment and long-segment fusion groups were higher than those before surgery, and the JOA score of the short-segment fusion group was higher than that of the long-segment fusion group (P < 0.05). The ODI score was lower than that before surgery in the short- and long-segment fusion groups, and the ODI score in the short-segment fusion group was lower than that in the long-segment fusion group (P < 0.05). At the 6th month after surgery, the pain scores of the lower back and lower limbs in the short- and long-segment fusion groups were significantly higher than those before surgery (P < 0.05). There were two cases of dural tears during decompression caused by lamina dura adhesion in the long-segment fusion group, and no serious complications were observed in the short-segment fusion group. Conclusions Both short- and long-segment decompression fixation fusion using a posterior approach can achieve good therapeutic effects for treating degenerative lumbar scoliosis. However, compared to the long-segment fusion group, the short-segment fusion group undergoing short-segment decompression fixation fusion through a posterior approach had a shorter surgical period, lower intraoperative blood loss, better recovery of lumbar function, and a lower risk of postoperative complications.