Delay Tolerant Network (DTN) is a new type of network, which is different from traditional TCP / IP communication protocol network. It is suitable for extreme environment where end-to-end communication connection cannot be established stably. Firstly, the characteristics and structure of DTN are analyzed, then the characteristics of nodes in the network are also analyzed. Secondly, the DTN routing problem is explained. Next, the classification of DTN routing algorithms and some classical routing algorithms are introduced. Finally, some other problems of DTN are proposed. The stable operation of the TCP/IP protocol relies mainly on three underlying link features: (1) There is a stable and reliable end-to-end link between the source node and the destination node; (2) The maximum round trip time RTT (Round Trip Time) between any nodes is not long; (3) The probability of message loss during transmission is low [2]. DTN extends the application of IPN to terrestrial mobile communications, emergency communications, underwater communications and wildlife monitoring. DTN can make up for the shortcomings of existing communication networks and realize communication connections in extreme or special environments. In recent years, research on DTN has made great progress. Further in-depth research on the DTN network in the future will inevitably promote and promote network communication.