GPS Navigation system plays an important role in reality, but its limited usability and discontinuous navigation capacity make it unfavorable for future use. To solve these problems, a new over-the-horizon navigation system which consists of three geo-stationary satellites and an aerostat was proposed. The optimization of constellation geometry for this system was also discussed based on minimum probability ellipsoid volume principle. Simple and effective constellation geometry was proposed after theoretic derivation. Simulation results verify the conclusion. This constellation strategy doesn't need matrix operation, thus has applicable value in reality.