Abstract: For the demanding of virtual assembly design,the currently available commercial VR software development toolkits have certain limitations,which make them difficult for use in virtual assembly （VA）. This paper identifies the limitations,and presents a Virtual Assembly Model （VAM） structure to diminish address the drawbacks.VAM is a multiple hierarchy structure.Based on commercial VR software and VAM,the paper investigates some key steps and applications of virtual assembly,such as assembly path,sequence planning,constraint relationships etc.,which are necessary for assembly design.