[objective] to investigate the key points and clinical efficacy of precise decompression technique for ossification of ligamentum flavum (OLF) in different pathological sites treated by posterior lateral percutaneous endoscopy of the spine.[methods] a retrospective analysis was conducted on 23 cases of thoracic OLF treated by posterior percutaneous spinal endoscopic approach in our hospital from September 2017 to November 2018, including 13 males and 10 females, aged 37-71 years with an average age of (53.0±9.9) years.According to the lesion site of OLF, there were 3 groups: 7 cases in the unilateral group (involving the unilateral lamina), 10 cases in the bilateral group (involving the bilateral lamina), and 6 cases in the fusion group (involving the bilateral laminae melting into one through the midline of the spinal canal).CT was reexamined after surgery to measure the proportion of ossification of the yellow ligament before and after surgery and to measure the degree of facet joint defect.1 month, 6 months and the last follow-up after the operation, the clinical efficacy was evaluated by using the visual analogue scale (VAS, the same below), JOA spinal cord function score (11-point method) and improved MacNab.[results] the follow-up time was 13-27 months, with an average follow-up time of 17.53±9.78 months.The proportion of ossified yellow ligament in 23 patients before surgery was 30.71%-73.27%, with an average proportion of (58.62±13.53) %.The proportion of ossified mass of the yellow ligament after surgery was 0%-20.47%, with an average proportion of (9.65±8.41) %.Postoperative degree of facet joint defect: 0%-37.53%;Average defect degree :(8.11±10.95) %.VAS score was (7.00±0.82) and (1.29±0.49) in the unilateral group at preoperative and final follow-up, respectively.In the bilateral group, the score was (7.20±0.92) and (1.60±0.70).Fusion group (7.33±1.03) points, (2.17±0.41) points.The differences were statistically significant (P < 0.001).Before and at the last follow-up, JOA score was (6.14±1.35) and (10.43±0.53) in the unilateral group, respectively.In the bilateral group, the score was 5.70±0.95 and 10.00±0.67.Fusion group (4.83±0.98) points, (9.67±0.82) points.The differences were statistically significant (P < 0.001).The excellent and good rate of improved MacNab was 91.30%.[conclusion] accurate decompression under percutaneous spinal endoscopy should be mainly decompression through lamina instead of intervertebral space window decompression, decompression from the periphery to the pressure-induced center, and bilateral decompression on the ipisional or contralateral unilateral approach at the lesion site is safe and reliable.Under the microscope, the grinding drill can be applied to the surface of the dural membrane to remove the ossification and adhesion of the yellow ligament.Facet joint defects were less than 50%, which did not affect the stability of thoracic vertebra.