The term “systemically important” frequently appears in every medium after 2008 financial crisis. Assessment of ”systemically important” is the necessary condition for regulating systemically important financial institutions. This paper is centered on the word ”Systemically important”, reviews how international world defines this word and its determining factors, and discusses international practices from quantitative and qualitative dimension on the assessment of ”systemically important”. Finally this paper gives advice on the crisis management arrangement of systemic important financial institutions.