The Japanese government has made nuclear security once again a hot topic by directly discharging contaminated water from the Fukushima nuclear power station into the Pacific Ocean. As nuclear security is a kind of interwoven security， mainly including the connotations of nuclear safeguard， nuclear safety and nuclear security， Fukushima nuclear safety accident and discharge of contaminated water into the ocean mainly related to the second level. Japan's discharge is a kind of heterogeneous non?traditional security threat with various characteristics. The current comprehensive governance mechanism， on the one hand， is based on international organizations represented by the United Nations and its subsidiary agency， the International Atomic Energy Agency， and on the other hand， a series of international treaties or conventions， including the Convention on Nuclear Safety. However， Japan's behavior reveals that the current nuclear safety governance mechanism is facing insufficient binding force and governance failure. In the future， mankind needs to strengthen nuclear security governance in terms of value matching， conceptual integration and joint action， making an concerted effort to build "a community with a shared future on nuclear security".