The security of overseas investment is a crucial guarantee for improving its performance, an important manifestation of the overall national security concept in the field of foreign investment, and a fundamental foundation for China’s path to stable and sustainable modernization. Under the overall national security concept, this paper constructs an index system for China’s overseas investment security and conducts measurement and evaluation to explore the mechanisms, economic effects, and pathways of international sanctions on China’s overseas investment security. The results indicate that in recent years, the level of China’s overseas investment security has first risen and then declined, with regional differences being the main source of the overall gap in China’s overseas investment security; international sanctions significantly suppress China’s overseas investment security, a conclusion that remains robust after testing and addressing endogeneity issues; this inhibitory effect exhibits heterogeneity, being more pronounced for high-income countries, middle- and low-income countries, and non-Belt and Road countries. International sanctions suppress the security of China’s overseas investments through three mechanisms: abrupt changes in the institutional environment, reshaping of geopolitical power, and obstruction of trade cooperation. As host countries’ financial stability improves, the inhibitory effect of international sanctions on China’s overseas investment security weakens, but the moderating variable of institutional distance between host countries and China intensifies this effect. With changes in host countries’ political stability or state governance, international sanctions exhibit clear threshold effects, spatial spillover effects, and spatial threshold effects on the suppression of China’s overseas investment security. The paper’s conclusions provide new perspectives, ideas, and approaches for maintaining the development and security of China’s overseas investments, coordinating and strengthening the protection of China’s overseas interests, improving the institutional mechanisms for safeguarding China’s national security, and advancing the modernization of the national security system and capabilities. It also offers empirical evidence and policy insights for actively and effectively mitigating various international sanctions risks and challenges under the overall national security concept, improving anti-sanction, anti-interference, and anti-“long-arm jurisdiction” mechanisms, and resolutely safeguarding national sovereignty, security, and development interests.