The People’s Bank of China and other departments jointly issued the “Guiding Opinions on Improving the Supervision of Systemically Important Financial Institutions” in 2018，which is a preliminary exploration of establishing a systemic financial institution supervision in China，to prevent systemic financial risks and improve China’s macroprudential supervision. The system has taken an important step. Based on the research progress and regulatory practice of systemically important financial institutions at home and abroad，this paper establishes a comprehensive system valuation system and calculation method for securities companies from five aspects：institution size，relevance，substitutability，complexity and asset realization. For the first time，the systemic importance of 131 securities companies nationwide was ranked and analyzed. The study found that：First，the systemic importance of China’s securities companies is seriously divided，the systemic importance scores are large，and the central concentration is high. CITIC Securities，Haitong Securities，and Huatai Securities are the top three systems of securities companies in 2018. Secondly，there is a close relationship between securities companies in China，securities companies and other institutions such as banks. Securities companies with lower systemic importance may have group risks due to their relevance，which will further trigger a systemic financial crisis. In supervising large securities companies，regulators should also pay attention to supervising the group risk of small and medium-sized securities companies and establish a comprehensive macro-prudential supervision system.