Abstract: Firstly, the technical features and modemization process of American GPS are analyzed in detail in this paper. Secondly, the current status and shortcoming of Russian GLONASS system are described and the differences between GLONASS and GPS are also discussed. Meanwhile, the development and associated techniques of European Galileo system are introduced. Finally, it expounds that the Beidou satellite navigation system is not able to better meet many users' requirements in China yet. Thereby, the system frameworks and key techniques for developing the second generation satellite navigation system of China are presented preliminarily.