The nodes of BOM may appear repeatedly in the different layers. While the structure of traditional tree model can not express the relation between these nodes expediently. By analyzing the localization of tree model BOM, this paper studies the essential structure of BOM and puts forward the drected-gragh with weightings of BOM. Then it provides corresponding realization of relation database and studies the method of maintenance. It also discusses the expansion of attribute based on enterprise' s requirement. Finally it provides the thinking of searching, relevant algorithm and the method of programming language realization. This kind of BOM offers foundation for the integration of information and data in PDM/CAPP/CIMS/ERP.