Abstract: The emergence of knowledge broker makes it possible to cross the "Caplan Gap" between academia and politics, which hinders the translation of knowledge into policy. Then, what is knowledge broker? How does it facilitate the transformation of knowledge into policy? The paper first explores the origins, connotations and types of knowledge broker, and then explores the knowledge management function, bridging function, two-way capacity building function, coherence seeking function and knowledge navigation function of knowledge broker in the alignment network linking academia and politics from the perspective of "structural hole" theory. However, knowledge broker also faces three highly challenging and controversial issues, namely, vulnerability, double marginality, and moral hazard. Theoretically clarifying the issue of knowledge broker has important implications for bridging the "last mile" from academic research to public policy in China.