Celestial navigation system has the advantages of high positioning precision and simple and reliable equipment. It is independent of local, space and time. The errors of positioning and orientation don’t accumulate and increase with time and distance. And it is free from being interfered or destroyed artificially. Also, it has the characteristics of well-concealing，high reliability and strong survival. With all of excellence, celestial navigation system has been used in the navigation and guidance of marine, aviation and space field. The paper describes the development trend and key technologies of celestial navigation system.