If the autonomous navigation techniques are applied to a navigation constellation, the number of the ground control stations, the message injecting frequency from the ground stations to satellites and system maintenance cost may be reduced significantly. Meanwhile, the integrity of navigation messages can be monitored in the real-time mode and the survivability of the navigation system also enhanced. The autonomous navigation will be gradually a main research subject for the next generation navigation satellite system. Firstly, the information processing flow of the autonomous navigation constellation is described systematically in this paper. Secondly, the key techniques to realize the autonomous navigation for the navigation constellation, including the long-term prediction of the ephemerides and clock parameters, establishment and maintenance for the cross measurement and communication links, autonomous time synchronization, autonomous ephemeris updating, robust filtering, establishment of the constellation rotation models, long-term prediction of the earth rotation and polar drift parameters, are presented as an important part of the paper. Moreover, the approaches to actualize the key techniques are analyzed and the relative mathematic models are also demonstrated in detail. Finally, the autonomous time synchronization and ephemeris updating are simulated. It is clearly shown from the simulated results that by processing the inter-satellite measurement data with the on-board Kalman filters and updating continually the clock parameters and ephemerides, the time synchronization and ephemeris updating among the satellites can be implemented autonomously and highly-accurately. Therefore, the reasonability and feasibility of the information processing flow and key technical algorithms for the autonomous navigation constellation are validated preliminarily.