Abstract: Data has emerged as a new type of production factor following traditional factors such as land, labor, capital, and technology. The integration of data into social production and service to generate new knowledge and economic value marks the process of realizing data value. Compared to traditional production factors, data exhibits characteristics of non-competitiveness and partial exclusivity. Therefore, the key to realizing public data value lies in achieving network effects and economies of scale through integrated use, public use, and multiple reuse. Cities are macro platforms and institutional domains for data generation, aggregation and circulation. Enhancing the knowledge production efficiency from massive public data in urban settings is imperative for the development of the digital economy. However, the overall mechanism of realizing the value of urban public data, particularly the role of the government, has not been sufficiently theorized. This study aims to identify the mechanisms and governmental roles that drive the value transition from data to knowledge in the realization of urban public data. Beijing, as a pioneering city in developing the digital economy and establishing the data market, serves as the case of this study. To ensure the reliability and validity of the case study, we employ a triangulation approach involving multiple sources of evidence, including field research, semi-structured interviews, policy documents, and statistical data. Based on the case study of Beijing, this research reveals that local government employs two mechanisms, "technological enablement" and "institutional empowerment," to address challenges in data value realization. Technological enablement refers to enhancing the data generation and application capabilities of relevant entities through digital technologies. Institutional empowerment involves defining responsibilities, rights, and interests among various actors through laws, regulations, and policies, providing legitimacy and action incentives. Technology and institutions interact dynamically, mutually relying on each other, where institutions provide legitimacy and public value for technology application, while technology supports the implementation of institutions. The government's role evolves throughout the process of data value-added. In the processes of data production, aggregation, and the transformation of data into information, the government addresses challenges such as limited data scale, dispersed distribution, and privacy concerns by providing generic infrastructure and institutional standards. As information transforms into knowledge, the autonomy of the market become increasingly significant. The government primarily empowers the market through mechanisms such as scenario openness and service procurement. It is noteworthy that, in practice, local governments tend to rely heavily on technological enablement, while the empowering role of institutions remains inadequately utilized. This results in fragmented and incoherent utilization of urban public data. Additionally, the lack of sound institutional frameworks contributes to a certain degree of a "omnipotent government" tendency in current local government practices, potentially inhibiting the autonomy of market entities. This paper contributes by using city as analytical unit, identifying the overall mechanisms of urban public data value realization, and elucidating the evolution of government roles. It expands the theoretical and empirical perspectives on the realization of public data value, providing insights for promoting the development of data market and building a strong digital economy.