The formation of economic linkages between firms through common shareholders has become a common phenomenon in capital markets. Existing research has primarily focused on the direct impact of common shareholders on a single firm, ignoring whether other firms within a shareholder network are affected when a particular firm faces exogenous policy shocks. Based on the establishment of an intellectual property court as a research scenario, this paper explores whether the rise in the level of intellectual property protection in the region of a firm with common shareholders' holdings affects the innovative behavior of other firms with common shareholders' holdings. The study finds that when an intellectual property court is established in the region, the innovation output of other firms within the same shareholder network increases significantly, indicating the existence of innovation synergies within the network of common shareholders. Mechanism tests show that common shareholders promote corporate innovation mainly by enhancing corporate R&D investment and promoting patent citations among firms in the network. Heterogeneity analysis indicates that the effects are more pronounced when firms are located in regions with weaker intellectual property protection, when shareholders are more actively involved in governance, when firms are less similar to those in pilot regions of intellectual property courts, when firms face higher financing constraints, and when they possess stronger knowledge absorption capabilities. The findings of this study not only expand the research perspective of shareholder network, but also helps to recognize the important role of intellectual property protection more comprehensively, and provides useful insights on how to better promote enterprise innovation and cultivate new quality productive forces.