R Social organizations are important participants in purchasing services，and there has been little research on strategies for cooperation between social organizations and mass organizations with both political and social attributes. Based on the perspective of multiple institutional logics，this study analysis the process of the cooperation between S social work institution in G City and the Communist Youth league in T District，it is found that the cooperation between social organizations and mass organizations faces a complex institutional environment of ideological guidance，administrative governance and professional services. Under the logic of ideological guidance，social organizations deepen their service areas by leveraging the resource platforms of mass organizations, ensuring that both parties form a joint force in ideological guidance work；under the logic of administrative governance，social organizations promote cooperation with mass organizations through demand driven，strategic autonomy，and two-way expansion；under the logic of professional services，social organizations focus on adding value to project effectiveness and integrating service resources，and ensuring the diversification of services. This study provides reference for enhancing the understanding of the cooperation between social organizations and mass organizations.