Abstract: 【Abstract】 Objective To compare the effectiveness of two lumbopelvic fixation procedures for treating unstable sacral fractures. Methods The clinical data of 47 patients were treated for unstable sacral fractures in the West China Hospital of Sichuan University from January 2010 to December 2014 were reviewed. Twentytwo patients (28 sides) were treated with USS combined with iliosacral screw (group A), while 25 patients (39 sides) were treated with closed multiaxial screws (CMAS) iliosacral fixation system combined with Posterior Segmental Spinal Fixation system (group B). The outcomes of the two procedures were compared using the following indicators: length of operations, amount of intraoperative blood loss, MATTA score of fracture reduction, MAJEED function score one year postoperation, postoperative complications, and GIBBONS Classification of sacral nerve injury in patients with sacral nerve symptoms. Results Group A had longer operations 〔(121.4±5.1） min〕 than group B 〔(110.6±4.5） min, P<0.05〕. Group A had larger intraoperative blood loss 〔(618±45） mL〕 than group B 〔(570±40） mL, P<0.05〕. Both groups had two cases of wound infection after operations that were cured by debridement and antibiotic therapy. According to the MATTA scoring criteria, group A had 92.9% excellent and good fracture reduction, compared with 97.5% in group B ( P<0.05). According to the MAJEED functional scoring criteria, group A had 86.4% excellent and good clinical functions, compared with 92.0% in group A ( P<0.05). The GIBBONS criteria indicated that neurological functions of both groups improved significantly after operations ( P<0.05), but no significant difference appeared between the two groups ( P>0.05). Conclusion CMAS iliosacral fixation system is better for treating unstable sacral fractures compared with USS combined with iliosacral screws.