Abstract: The purpose of the safety classification is to ensure that items are designed, manufactured, constructed, tested and operated with appropriate requirements to ensure that items have the appropriate quality under all expected operating conditions and to ensure the realization of safety functions. The Safety Classification of Structures, Systems and Components (SSC) in Nuclear Power Plants (SSG-30) was issued in 2014 by the International Atomic Energy Agency (IAEA). The principle of the safety classification covers five defense levels of nuclear power plants. It identifies the importance of safety-related items from two dimensions of design provisions and function categorized, considers the requirements of operating conditions and radioactive and operational limits of nuclear power plants, and determines the safety classification of items and related code requirements.