Commercial health insurance is an important component in the construction of a multi-level healthcare security system. This study takes the social-commercial cooperation in critical illness insurance for urban and rural residents as the entry point, reveals the key issues of participation of commercial insurance in the critical illness insurance operation and analyzes the causes, through field research and a comprehensive analysis of the critical illness insurance operation and social-commercial cooperation models in sample regions. The study finds that while the critical illness insurance system has effectively alleviated the financial burden on patients with severe illnesses, it still faces numerous challenges, including unclear boundaries of stakeholder responsibilities, unequal distribution of profit and loss risks, inadequate incentive mechanisms, and unresolved information barriers. Based on these issues, this study proposes recommendations such as strengthening top-level design to clarify the functional positioning of stakeholders, improving cooperative mechanisms to fully leverage the advantages of commercial insurance, and optimizing supply-demand matching to reinforce the supplementary role of commercial insurance. These suggestions can provide practical insights and decision-making references for promoting the participation of commercial insurance in the construction of a multi-level healthcare security system.