Interoperability is the most important objective of IEC 61850. Model design and realization are critical steps to achieve the objective. Based on an analysis of interoperability support， a universal design method of IED model is given， and problems in realization of bay level IED model are discussed. Bay level IED is an embedded system， whose information models are realized in the form of data structures. The advantages and disadvantages of several data structures considering interoperability are examined. On this basis， a new data structure named ASCI-FC data structure is designed， in which functional constraints（FCs） are included while the hierarchical structure of information model is retained， thus better supporting interoperability. Data storage structures making use of the binary or ternary chain list are given. Examples prove their advantages at object locating and data traversing. A FC filtering method for ASCI-FC data structure stored in binary or ternary chain lists is also given to show the advantage of this data structure.