Abstract: DTN (delay-tolerant network) is an abstract network model that comes from some mobile self-organized networks such as ad hoc, WSN (wireless sensor network), satellite networks, etc. Its main characteristic is that the links between nodes are volatile and may break down for a long time at any time, so the network always suffers from long time partitioning. Being different from ad hoc, the partitioning in DTN may last such a long time that it can't be assumed that a path exists between the source node and destination node in DTN. DTN is proposed to deal with these situations. As a network model, routing algorithm is the pivot problem in those such as system architecture, packet format, neighbor discovery, etc. There have been many studies on routing algorithm in DTN, but there is still no mathematical model to analyze the delay which is the most important metric in most routing protocols. In this paper the procedure of delivering a packet in one hop in DTN is studied, and then a model is constructed for analyzing this one-hop delay. Finally queuing theories are used to give some important results which show the relations between some parameters such as average delay, average queue length and traffic distribution etc. Simulations prove that the results match the simulation situation.