Abstract: The new BBNJ Agreement established the system of strategic environmental assessments in areas beyond national jurisdiction(ABNJ). European and American countries first defined strategic environmental assessments through domestic laws, thus reclaiming the “right to define” in the new international treaty. The introduction of marine strategic environmental assessment is of great significance for the protection of biodiversity in ABNJ. However, it also faces many challenges such as the diversification of the connotations and practices of strategic environmental assessment, fragmentation of international rules on SEAs, and internationalization of implementing entities. China should fully recognize the role and characteristics of strategic environmental impact assessment as a procedural mechanism in environmental governance in ABNJ, improve the domestic law and practice of SEA, and lead the construction of a maritime community with a shared future and the discourse power related.