Virtual assembly system requires higher accuracy on collision detection than ordinary virtual reality application. Based on analyzing the requirement of virtual assembly on accurate collision detection, a kind of hierarchical accurate collision detection thought is proposed, which includes three levels: assembly environment level, polygon level and accurate geometry topology model level. Three ways for virtual assembly system to obtain accurate geometry topology model are given. A specific solution that synthetically uses geometry graph supporting toolkit to realize hierarchical accurate collision detection is presented. A comparison experiment manifests that above solution and approach are feasible and efficient.