Abstract: The self-judging essential security interest clause under international investment agreement is an edge tool for safeguarding host state's national security and sovereignty. The function of self-judging essential security interest clause is formed on the basis of its text and context， and determined by the standard of review adopted by international arbitral tribunals. Due to current divergence regarding the standards and approaches in conducting good faith review by international arbitral tribunals， the de facto function of such clause has remained uncertain. The standard of review adopted by the Dispute Settlement Body of the WTO in reviewing the Article XX of GATT， the margin of appreciation adopted by the European Court of Justice and the standard of review adopted by domestic administrative courts in judicial review could provide beneficial models to the international investment tribunals in conducting good faith review. This Article argues that China shall form and improve the self-judging essential security interest clause on the basis of a profound understanding of its standards and approaches of review as well as its de facto function， while embedding the value of balancing the national security interest and investor's interest.

Key words: self-judging clause, essential security interest, international investment agreement, good faith review