Abstract: Objective: To compare the blood vessels' distribution in "iliac blood vessel triangular area" and "lateral safe region" of the lumbosacral vertebrae and the range of "effective working area" after operation,so as to provide anatomic data for lumbosacral anterior operation.Methods: The range of "iliac blood vessel triangular area" in common condition and "iliac blood vessel triangular effective working area" after laterally dragging iliac blood vessels,the range of "lateral safe region" in common condition and after safely dragging lumbosacral vertebrae anterior blood vessels and the "lateral effective working area" after ligating lumbar segmental vessels were observed and compared in 30 human cadavers.Results: The area of "iliac blood vessel triangular area" in common condition was(785.85±333.91) mm²;the area of "iliac blood vessel triangular effective working area" after laterally dragging iliac blood vessels was(938.97±351.39) mm²;at L₅-S₁ level,the left range of "lateral safe region" in common condition was(148.44±64.40) mm² and the right range was(142.45±46.66) mm²;after safely dragging lumbosacral vertebrae anterior blood vessels,the left range of it was(178.76±72.97) mm²,and the right range was(178.59±60.54) mm²;after ligating lumbar segmental vessels,the left range of "lateral effective working area" was(314.80±82.47) mm² and the right range was(322.12±73.68) mm².Conclusions: It is proper to select "iliac blood vessel triangular effective working area" approach when carrying out anterior operation of L₅-S₁.This area can satisfy the space requirement of single rod-screw or single screw-plate during internal fixation.