Abstract: On the authors' opinion,there exist two types of network objects:nodes and arcs.But the relations between network objects are complex.Both topological and connecting relations between network objects should be represented completely when the data structure for GIS networks is designed.And the structure should accord with the requirements for a general GIS data structure.In addition,the structure should be efficient for network analysis.Firstly,this paper analyses the problems when connecting relations are absent in a data structure for GIS networks.The topological relations are simplified on combination with the frame of the four-intersection-model for topological relations and the characteristics of a GIS network.Five types of basic topological relations are summarized.Then,this paper presents a new data structure for GIS networks,TDN structure,with both types of relations.In the new data structure there are two types of network objects,nodes and arcs.Both of them are composed of semantic elements and geometric elements.There exist four types of semantic elements and three types of geometric elements.Lastly,this paper analyses the efficiency of TDN structure.In TDN structure,the maximum calculating time to find a nearby node for current node equals to the number of arcs that are connected with the current node.Apparently,the structure is more efficient than adjacency matrix structure.This paper also analyses the storage efficiency of the data structure.An expriment shows that the data structure is applicable and reliable.