Although often not explicitly stated, the existing Internet model is based on a number of assumptions, such as: an end-to-end path exists between the source and its destination at all time, the maximum delay is not excessive, and the packet drop probability is small. However, a class of challenged networks, which are called DTN (delay/disrupton-tolerant network), emerge in many circumstances. DTN is greatly different from the traditional network model. It has long delay, frequent disruption, no end-to-end path simultaneously, and the network nodes have the capability of limited storage/processing. As a result, the present network protocols, such as Transfer Control Protocol (TCP), can not satisfy the applications over DTN. Some recent advanced researches in DTN are reviewed in this paper. Firstly, the main organizations working on DTN topic and typical characteristics of DTN are introduced. Then several classical overlay protocols of DTN are presented, such as bundle protocol, and some routing algorithms, including single copy routing algorithms based on knowledge and multicopy routing algorithms, are compared. Moreover, DTN researches in deep space communication, ferine animal, water quality survey and remote village connecting with Internet are discussed as real examples of DTN. Finally, the open issues and challenges of DTN in near future are proposed.