Space-Air-Ground Integrated Network is the trend for 6G network development. It could integrate many advantages from terrestrial network, satellites and high altitude platform stations, improving the coverage and service quality significantly. Meanwhile, breaking the barriers of heterogeneous networks and realizing the cooperation between them pose new challenges for network operation. This paper firstly analyzes the current situation and expounds technical researches and commercial achievements from the perspectives of standardization and industry. Secondly, we focus on network architecture, network sharing and private network, mainly investigating the operation and mutual enabling key technologies in Space-Air-Ground Integrated Network. Finally, we point out the challenges from “time-frequency-space” dimensions.