Objective To observe and measure the approach next to the erector spinae in the thoracic and lumbar segments of the spine and adjacent anatomical structures by the topographic method, to clarify the positioning method and safe range so as to provide the anatomical basis of the approach for spinal canal decompression. Methods Twelve formaldehyde-treated adult cadaver specimens were selected, including 6 males and 6 females with an average age of 43 years (range, 27-52 years) and with an average height of 166 cm (range, 154-177 cm). The related data of the approach at T1-S1 levels were respectively measured: the distance between the lateral edge of the erector spinae and the spinous process, the length of the approach, the angle between the approach and the horizontal plane, the size of intervertebral foramen, and the vertical distance between the segmental artery and the upper edge of the vertebrae. Results The distance between the lateral edge of the erector spinae and the spinous process ranged from (41.75 ± 3.29) mm to (74.54 ± 7.08) mm. The length of the approach ranged from (66.75 ± 10.81) mm to (97.13 ± 13.35) mm. The angle between the approach and the horizontal plane ranged from (38.38 ± 6.16)° to (53.67 ± 4.40)°. The vertical distance between the segmental artery and the upper edge of the vertebrae ranged from (9.50 ± 0.60) mm to (18.30 ± 1.56) mm. The size of foraminal was also measured. The spinal canal could reach when iliocostalis lateral edge was used as the starting point in the lumbar segments, and longissimus lateral edge as the starting point in the thoracic segments. It was confirmed that there was enough safe space for the spinal decompression without the resection of the articular process. Conclusion The approach next to the erector spinae can reach spinal canal to achieve the purpose of decompression through the intervertebral foramen. The minimally invasive approach is feasible and safe. It has the value of the operative application.