Objective    To study the effects of Ⅰ~Ⅱ degree lumbar spondylolisthesis on the left lumbar segmental vessels  and the safety zone of OLIF surgical access by MRI.    Methods    The MRI data of lumbar spine of 221 patients with low back and leg pain who met the selection criteria from October 2019 to November 2022 were retrospectively analyzed, and patients with lumbar disc herniation, discogenic low back pain, and degenerative lumbar spinal stenosis without significant collapse of the intervertebral space height and without intervertebral displacement were divided into the control groups (n=107). Patients with I～II degree lumbar spondylolisthesis  were divided into the observation group (n=114). The angles of vascular emanation from the lateral segments of the left vertebral , the angles of vascular travel, the length of the vessels, the spacing of the vessels in the segments of different Moro regions of the vertebral and their distance from the adjacent disc edges were measured and compared between the two groups. The differences in the area between segmental vessels and the proportion of vessels present in the simulated channels were also analyzed.     Results     ① Compared with the control group, the angle of L4 vessel emanation, the angle of L1/L3/L4/L5 vessel travel, and the length of L2/L4 vessels were reduced in the observation group, and the distance between the vessels of L1,2 and L3,4 segments was decreased at the junction of II-III and III -IV zones, and the intervascular area was reduced accordingly. ②The area between the L4,5 vertebral segmental vessels was<22mm at the junction of the III-IV region in  both groups .The distance between the segmental vessels and the edge of the same sequence of vertebral bodies is<10 mm in the two groups,except the distance between the L3-5 vessels with the same sequence of lower edge in the I-II region. In addition, the results of the same sequence of vertebral artery distances from the lower edge of the vertebral suggested that the distances at the junction of L1 II - IV zones decreased, but the distances at the junction of L4 II - IV zones increased, while the results of the same sequence of vertebral vein distances from the upper edge of the vertebral suggested that the distances at the junction of L2 I - II zones, L2-5 II - III zones, and L2/L4 III - IV zones decreased. ③ The proportion of lumbar segmental vessels in the simulated channels was greater in the observation group than in the control group, with the most significant differences found in the L5 vessels in zones I and II.    Conclusions    Ⅰ～Ⅱ degree lumbar spondylolisthesis affect the travel of the left lumbar segmental vessels, reduce the distance between segmental vessels in L1,2 and L3,4 , narrow the distance from the L2-5 segmental vessels at the junction of zones II-III to the upper edge of the vertebral in the same sequence, increase the difficulty and risk of OLIF channel establishment. In particular, when operating in the L4,5 interval, it is necessary to avoid placing OLIF expansion channels at 10 mm from the disc edge and at the junction of zone III-IV. The channels can be adjusted to the cephalic side of zone II as appropriate, and close attention should be paid to the alignment and distribution of the vessels of the L5 segment in zones I and II to avoid injury.