Objective To compare the clinical efficacy between unilateral biportal endoscopy (UBE) technology and open surgery in the treatment of lumbar spinal stenosis (LSS) and their effects on spinal stability. Methods A retrospective analysis was conducted on 90 patients with LSS who underwent surgical treatment at Longyan Second Hospital in Fujian Province from January 2021 to January 2024. The patients were divided into two groups based on the surgical approach: the endoscopic group (n=45) and the open group (n=45). The two groups were compared in terms of surgical indicators (surgical duration, intraoperative blood loss, hospital stay, and postoperative drainage volume), fusion outcomes (fusion time, CT fusion grading), Visual Analogue Scale (VAS), functional indicators [Oswestry Disability Index (ODI), Japanese Orthopaedic Association (JOA) score], and spinal stability imaging parameters (intervertebral flexion-extension angle, segmental slippage distance). Results The endoscopic group demonstrated significantly superior outcomes compared to the open group in terms of surgical duration, intraoperative blood loss, hospital stay, and postoperative drainage volume (all P<0.001). At 12 months postoperatively, there was no statistically significant difference in fusion grading between the two groups (P=0.419), and there was no significant difference in fusion time between the two groups (P=0.393). At all postoperative time points, the endoscopic group had lower VAS scores for low back pain than the open group (P<0.05), while there was no significant difference in VAS scores for leg pain between the two groups (P>0.05). The ODI in the endoscopic group was significantly lower than that in the open group at 12 months postoperatively (P<0.05), while there was no significant difference in JOA scores between the two groups (P>0.05). At 12 months postoperatively, the endoscopic group retained more physiological mobility at the surgical segment [(2.8±1.0)° vs. (1.9±0.8)°, P<0.001], and the angle change value was smaller than that of the open group [(7.4±2.5)° vs. (8.6±2.8)°, P=0.035]. At 12 months postoperatively, the endoscopic group had a significantly greater segmental slippage distance [(0.8±0.3) mm] than the open group [(0.5±0.2) mm] (P<0.001), but there was no significant difference in the change in slippage between the two groups (P=0.450). Conclusion UBE technology for the treatment of LSS is characterized by minimal trauma and rapid recovery. It is superior to open surgery in relieving patients’ low back pain and improving their quality of life, while better preserving the spine’s moderate physiological mobility. It is a safe and effective minimally invasive treatment method.