Autonomous entry navigation is of great importance for Mars precision landing. When designing a navigation system for Mars atmosphere entry, its observability should be given sufficient attention. Because the conventional measurements only using inertial measurement unit (IMU) cannot guarantee the full-state observability, dynamic pressure measurement assisted navigation scheme is introduced in this paper to make the navigation system more observable. Then, the observability of the introduced dynamic pressure measurement assisted navigation is firstly analyzed in detail with respect to axial direction of single dynamic pressure sensor. What is more, to further improve the observability of the navigation system, the configuration of triple dynamic pressure sensors is optimized considering different angle combinations of the axial direction of different dynamic pressure sensors and the direction of the velocity of the vehicle (incidence angle). The proposed configuration optimization method is demonstrated and validated through numerical simulation, whose results can demonstrate that the full observability of the navigation system can be guaranteed when this angle configuration is used.