Purpose: As a new channel for agricultural extension, university-based agricultural extension is changing the traditional pattern of agricultural extension in China. This study reveals the mechanism through which policy affects the performance of university-based agricultural extension. Design/methodology/approach: Based on Rhodes' policy network analysis, this study analyses the interactive relationships between the stakeholders in university-based agricultural extension. Taking 12 institutes of new rural development at agricultural universities in China as its sample, the study uses grounded theory to model the mechanism by which policies and policy changes influence the performance of university-based agricultural extension with a view to providing a new theoretical perspective and paradigm for research on university-based agricultural extension policies. Findings: The study reveals a self-reinforcement mechanism in the changes in university-based agricultural extension policies, and shows that path dependence has a normative effect on policy changes. Practical implications: University-based agricultural extension is of great significance to promoting reform and innovation in China's agricultural extension system, which features 'one core with multiple supplements'. Theoretical implications: The study reveals the influence of a more complex policy network composed of three levels of policy -- state, provincial, local -- on university-based agricultural extension, and expands the application of the policy network theory. Originality/value: The findings will guide the Chinese government in achieving its vision of creating the perfect mechanism for university-based agricultural extension.