Abstract: Version management is very important in engineering data management,and is a method to maintain consistency of design data.A notion of design object is proposed,based on which the design information of product is described.The composed relation,version relation,and equivalent relation are used to establish the relation design object.A version mechanism is established in the paper for engineering data management.A hierarchical model of design object is proposed.Some notions such as version history of design object,relations of version history of design object,and so on are proposed.A data model of version mechanism is established.Finally,the operation （check in/check out,selection of current version,dynamic configuration of version and so on） of version object is analyzed.