Objective To determine the variability of the anterior vascular anatomy at the lower lumbar spine and provide anatomic data for the design of L5/S1 anterior fusing plate.  Methods This study investigated 41 human cadavers (26 males and 15 females). The distance from the bifurcation or confluence to the top of L5/S1 disc and the width of operation window of L5/S1 disc (the distance from right common iliac artery to left common iliac vein) were determined.  Results The bifurcation level of the ventral aorta and the confluence level of the common iliac vein were showed from L4 to L5. The course of the ventral aorta was in the right front of vertebra and the course of the common iliac vein was in the left front of vertebra. The bifurcation angle of the ventral aorta averaged 62.8°

the confluence angle averaged 71.8°

and the right common iliac aorta and the left common iliac vein angle averaged 71.5°. The distance from the bifurcation to the top of L5/S1 disc averaged (3.8±1.0) cm. The distance from the confluence to the top of L5/S1 disc averaged (2.2±0.8) cm. The distance from the confluence of the right common iliac aorta and the left common iliac vein to the top of L5/S1 disc averaged (2.0±0.7) cm. Conclusion Because of the bifurcation level of the ventral aorta and the confluence level of the common iliac vein are over the top of L5/S1

the placement of internal fixation device and anterior L5/S1 fusion is safe in 95.1% people.