Abstract: The increasing demand on space communication stimulates the internetworking and space-ground integration for space communication systems. Space networks are featured in heterogonous subnets, dynamic topology, large transmission delay, and high link errors. TCP/IP protocol suite requires stable connectivity and short transmission delay, which cannot be satisfied in space networks. As a result, existing protocols for the current Internet cannot be directly applied to space networks. Delay/disruption tolerant network (DTN) is a general message-oriented overlay network architecture that can be adapted to space networks. This makes DTN a very promising approach for interconnecting space communication systems. This paper first demonstrates the system architecture which applies DTN in space internetworking service (SIS), and then analyzes the key components and working patterns including protocol stack, message forwarding mechanism, naming and addressing, licklider transmission protocol (LTP), etc. Then we give a real scenario of Mars exploration. By surveying some key technologies and research trends, we analyze some technical problems to be solved and propose some future research directions including routing, security, and QoS control. And then, we introduce related development efforts, practice, and aircraft verification projects. Finally, we analyze the prospects for the research and application of DTN and SIS technologies in China.