Abstract: In recent years, the multi-source and multi-dimensional services of ground networks and space networks present a trend of integration, and the increasingly mature space networks are gradually enhancing the complementary power of ground networks in terms of service capabilities. The significance of building an integrated network for 6G and future communication is far-reaching. Firstly, this paper introduces the concept of space-ground integrated network and describes three stages of the interweaving and integration development of satellite communication and ground communication. Then, it sorts out the current development status of typical space-ground integrated systems and communication systems of space-ground integrated network at home and abroad. By analyzing the development trend, vision, requirements and challenges of space-ground integrated network, three potential key technologies are identified, namely intelligent network technology, integrated air interface technology, and ultra high frequency technology which solves the large-scale heterogeneous multi network fusion, seamless switching between satellite networks and ground networks, and ultra-high bandwidth requirements of massive data communication. Moreover, analyzes and expounds the application of key technologies in the space-ground integrated network. In addition, it puts forward some suggestions for the development of key technologies in engineering applications for the space-ground integrated network.