Abstract: Against the backdrop of innovation-driven development strategy and the construction of a unified national market, this study empirically examines the impact of city clusters policies on inter-firm collaborative innovation. The findings reveal that: (1) city clusters policies significantly enhance collaborative innovation among enterprises within the same region by facilitating the flow and integration of technological factors; (2) the policies operate through three main channels—increasing government subsidies, strengthening intellectual property protection, and deepening specialization and industrial division of labor; (3) heterogeneity analysis indicates that the effect is more pronounced in regions with lower levels of social trust, weaker industrial agglomeration, and more intense market competition, with particularly strong impacts observed in cross-provincial and multi-core city clusters. These policies also significantly promote various types of collaboration, including “firm-firm,” “firm-university,” and “firm-research institute” partnerships; (4) the improvement in collaborative innovation further contributes to the growth of firms’ total factor productivity. This study provides empirical evidence and policy insights for reshaping enterprise innovation models amid the advancement of China’s unified national market.

Key words: city clusters, cooperative innovation, government subsidies, intellectual property protection, specialization