Abstract： Objective To study the variation and development of anterior communicating artery(ACoA) complex and their effects on the treatment of aneurysms. Method Sixty fresh fetal cadavers and their variations of ACoA complex were observed. Twenty-nine patients with ACoA aneurysms received clipping surgery and 49 patients received embolization treatment successfully. Results 1. There was Al fenestration in 2 cases and dysplasia type in 15 cases. All variations of ACoA consisted of fenestration in 12 cases, duplication in 5, Y-shaped in 4, median artery of the corpus callosum in 4, plexiform in one, H-shaped in one. There was no significant difference between complex variations and the gender and age of patients. There was no significant correlation between variations of Al and ACoA. 2. Al dysplasia or absence of 59 patients with aneurysm and ACoA variations of 3 patients were also observed. The necks of aneurysms were located on the apex of bifurcation of dominant Al. The middle segment of ACoA of 19 patients and the ACoA-A2 of 4 patients were also found. There was no death related to operative techniques. Conclusions The variations of ACoA complex consequently exist early in fetal development. However, the variations of Al dysplasia and single form of ACoA are observed in the patients with aneurysms. The operative techniques of dominant Al are used to improve the safety of the treatment.