Objective To compare the clinical efficacy of transforaminal lumbar interbody fusion under unilateral biportal endoscopy (UBE-TLIF) and traditional posterior lumbar interbody fusion (PLIF) in treating single-segment degenerative lumbar spondylolisthesis with lumbar spinal stenosis (DLS-LSS). Methods The clinical data of 85 patients diagnosed with DLS-LSS who underwent surgery between Jan. 2020 and Jan. 2022 in our hospital were retrospectively analyzed. Patients were assigned to UBE-TLIF group (46 cases) and PLIF group (39 cases) based on the surgical procedure. The general characteristics, perioperative data, radiological parameters, and clinical efficacy indicators were analyzed. Results There were no significant differences in baseline characteristics, preoperative radiological parameters, pain visual analogue scale (VAS) score, or Oswestry disability index (ODI) score between the 2 groups (all P＞0.05). Compared with the PLIF group, the UBE-TLIF group had significantly longer operation time (［156.42±26.65］ min vs ［141.36±21.46］ min, P＝0.006), significantly less operation blood loss (［170.15±10.87］ mL vs ［203.15±15.67］ mL, P＜0.001), and significantly shorter hospital stay (［6.73±2.42］ d vs ［9.61±2.56］ d, P＜0.001). The UBE-TLIF group had significantly smaller lumbar lordosis and segmental angle 3 months postoperatively (［42.52±8.57］° vs ［46.61±7.31］°, ［10.93±2.59］° vs ［12.16±3.05］°) and at final follow-up (［41.35±7.46］° vs ［44.62±6.42］°, ［10.65±2.43］° vs ［11.87±2.53］°) compared with the PLIF group (all P＜0.05). The fusion rate was significantly lower in the UBE-TLIF group compared with the PLIF group 3 months after operation (34.78% ［16/46］ vs 58.97% ［23/39］, P＜0.05), with no significant difference at final follow-up (93.48% ［43/46］ vs 94.87% ［37/39］, P＞0.05). The VAS score and ODI score 3 months after operation were significantly lower in the UBE-TLIF group compared with the PLIF group (2.43±0.92 vs 3.12±1.03, 26.81±9.14 vs 33.35±8.76, both P＜0.01), with no significant differences at final follow-up (both P＞0.05). Conclusion As a minimally invasive surgical technique, UBE-TLIF has the advantages of minimal trauma, fast recovery, mild postoperative pain, and a reliable fusion rate. It is an effective treatment for DLS-LSS and deserves to be promoted.