To observe the morphology character of the anterior epidural space at the L disc level and to provide an anatomical basis for safely and accurately performing a percutaneous endoscopic lumbar discectomy (PELD). Fifty-five cases with L S lumbar disc herniation were included in this study, and cases with L disease were excluded. When the puncture needle reached the epidural space at the L S level, iohexol was injected at the pressure of 50 cm H O during the PELD, then C-Arm fluoroscopy was used to obtain standard lumbar frontal and lateral images. The widths of epidural space at the level of the L lower endplate, the L upper endplate, as well as the middle point of the L disc were measured from the lumbar lateral X-ray film. Epidural space at the L disc plane performs like a trapezium chart with a short side at the head end and a long side at the tail end in the lumbar lateral X-ray radiograph, while the average widths of epidural space were 10.2 ± 2.5, 12.3 ± 2.3, and 13.8 ± 2.6 mm at the upper, middle, and lower level of the L disc. Understanding the morphological characteristics of epidural space will contribute to improving the safety of the tranforaminal percutaneous endoscopy technique.