Abstract: Link represents the relationship between objects and is a very useful construct for modeling database and subjective world. Based on the definition of object, the concepts of single link and batch link are presented, that are used to represent the relationship between object instances and the relational class among objects. The two kinds of link make link object reaching complete. The implementation of link in the engineering database management system is also presented and the applications of link in representation of complex object and fast querying etc. are discussed in detail.