Abstract: As space exploration enters the era of commercialization, an increasing number of private investors are actively participating in various space investment activities. However, due to the systemic deficiencies present in both international investment law and public international law, many space investment activities cannot be effectively protected under existing international investment treaties. Specifically, the qualification of investments remains uncertain, and the substantive treatment clauses fail to meet the practical needs of space investment. In public international law, both airspace and outer space suffer from institutional ambiguity and unclear jurisdiction over specific space activities by host countries. These deficiencies also constitute the underlying reasons why international investment law fails to provide effective protection for space investments. States should therefore prioritize the interplay between international investment agreements and public international law, promptly address systemic deficiencies, and thereby achieve effective protection for various space investment activities.