Innovation is recognized as a crucial driver of high-quality economic development and a key factor for enterprises to gain long-term competitive advantage. The board of directors, as the core entity responsible for formulating corporate strategy, influences the level of innovation in a company through the acquisition and utilization of innovative resources. Drawing on social network theory, the impact of informal internal board networks on corporate innovation and the moderating effect of external board networks were examined. Data from listed companies on the Shanghai and Shenzhen stock exchanges from 2013 to 2021 were utilized, and the research findings indicate that the informal internal board network, formed based on the "seven similarities" relationship attributes, significantly promotes corporate innovation. Additionally, the relationship between the informal internal board network and corporate innovation is positively moderated by the structural holes and centrality of the external board network. The study's conclusions not only respond to the academic call for the integration of demographic characteristics with the local context in China, but also reveal the interaction between internal and external board networks, deepening the understanding of the social network governance mechanisms in Chinese enterprises.