Objective:To investigate the mid-term efficacy of Dynesys internal fixation and posterior lumbar interbody fusion (PLIF) in the treatment of grade I degenerative lumbar spondylolisthesis.Methods:From June 2014 to June 2016, 68 cases, in which 35 males and 33 females aged from 44-74 (55.3±7.5), of grade I degenerative lumbar spondylolisthesis treated using Dynesys internal fixation were retrospectively analyzed. There were 8 cases of L 3, 52 cases of L 4 and 8 cases of L 5 with an average visual analogue scale (VAS) of 4.5±2.1. At the same time, 72 patients were treated with posterior lumbar interbody fusion (PLIF). There were 37 males and 35 females aged from 46-76 (56.8±7.2), with 9 cases of L 3, 53 cases of L 4 and 10 cases of L 5. The VAS of this group was 4.4±2.3. The operative time, intraoperative blood loss, postoperative drainage volume and complications were compared between the two groups. Range of motion (ROM), disc height of stable segment and upper adjacent segment, adjacent segment degeneration between the two groups were evaluated. ASD, Oswestry disability index (ODI) score and Japanese Orthopaedic Association (JOA) score were also compared between the two groups. Results:The patients in both groups were followed up. The follow-up time of Dynesys group was 50-74 months, average 64.2±18.3 months, and the follow-up time of PLIF group was 55-79 months, average 65.2±15.5 months. The operation time [(120.5±21.0) min vs. (132.5±27.0) min, t=2.924, P=0.004], intraoperative bleeding [(312.5±80.7) ml vs. (352.5±84.5) ml, t=2.861, P=0.005] and postoperative drainage [(120.3±45.8) ml vs. (140.2±50.2) ml; t=2.446, P=0.016] in Dynesys group were significantly better than those in PLIF group. The differences were statistically significant. There was no significant difference in postoperative ROM of stable segment, ROM of upper segment, disc height of stable segment and adjacent segment between the two groups before operation. At 5 years postoperatively, there was statistically significant difference between the stable segment ROM (4.3°±1.6° vs. 0; t=22.809; P<0.001) and the upper segment ROM (10.5°±2.1° vs. 12.8°±2.2°; t=6.329, P<0.001). At 5 years postoperatively, ODI scores of the two groups were (11.25%±8.12%, 16.53%±9.23%), and JOA scores were (22.60±2.20, 19.01±2.34), which were significantly improved compared with those before surgery, with statistically significant differences (ODI: t=3.585, P<0.001; JOA: t=9.340, P<0.001). There was no significant difference in the incidence of symptomatic ASD between the two groups (8.8% vs. 16.7%, χ2=1.284, P=0.257) , but there was significant difference in the incidence of X-ray ASD between the two groups (2.9% vs. 13.9%, χ2=4.043, P=0.044) . Conclusion:Compared with PLIF, Dynesys internal fixation for degenerative lumbar spondylolisthesis is a minimally invasive, safe and effective surgical method to retard ASD; Compared with PLIF, adjacent segment degeneration can be reduced using Dynesys internal fixation.