Abstract:     Smart city is the intelligent performance of innovative applications for information technology embedded in social service and management. Smart city pilot projects have gradually been included in 89% of provincial and sub-provincial cities whereas repetitive or conflicting construction has shown the potential negative impact on urban resource due to policy ambiguity, although the government has taken a series of measures to promote the smart construction process. Therefore, this paper establishes an analysis framework of policy instruments based on resource utility - technical structure - application field, text content analysis, social network analysis and multidimensional scale analysis are used to analyze the evolution of smart city policies, policy network relations, co-occurrence keywords from year 2011 to 2021. Meanwhile, explores the structural evolution process of supply-oriented, environment-oriented and demand-oriented policy instruments in IoT sensing platform policies, cloud computing industrial policies and smart application service policies in smart city. The main valid data set related to smart city policy document issued by the central state ministries and functional departments of local government are collected, and then analyzed through text content unit encoding, from which the following conclusions can be inferred.
    The first conclusion shows that smart city policy has experienced three evolutionary stages involving in perceptive infrastructure and top-level design stage, cultivation and innovation-driven stage of smart industry, and heterogeneous development of smart application field. In the first stage, the technical concept and architecture system of the Internet of Things are put forward; in the second stage, intensive promulgation and rapid development of core supporting technology are reflected, involving big data, artificial intelligence and other strategic emerging industry; and in the third stage, the application integration of smart government, smart medical and smart transportation are exhibited, gradually expanding to various application systems such as smart environment and security.
   The second one reveals that many independent network groups have developed in smart city policy network, early policies mostly focused on top-level construction of infrastructure in relevant to Internet of Things and gradually transferred to implementation in heterogeneous domain in terms of programmatic policy document.
   The third one points out the thematic evolution of smart city policy at different evolutionary stages. Policy theme at the first stage covering policy objectives, foundational technology, organizational security system, and policy theme at the second stage take consideration of synergy of industrial structure optimization and innovation resources, establishment of innovation environment, technology standardization and evaluation. Policy theme at the third stage means data fusion, heterogeneous smart application fields and policy effect.
   The fourth one expounds the structurally unbalanced in smart city policies, and compared with the supply-oriented policy instruments that were used steadily in the initial stage of evolution, environment-oriented policy instruments are steadily increasing, while demand-oriented policy instruments are dynamically matched. In comparison with the cloud computing support industry layer dominated by supply-oriented policy instruments, IoT platform policies tend to combine utility of supply-oriented and environment-oriented. smart application policies are adaptive coupled with environment-oriented policy instruments and further developed from government-oriented pattern to market-oriented collaboration, with public service, scientific and technological information support are frequently employed. IoT sensing platform policies emphasis on smart infrastructure, while cloud computing industrial policies are influenced by citizen participation mechanism, innovation and entrepreneurship measures with top-level design and regulations. Priorities of smart construction are adaptive to different evolutionary path of smart application fields from early technology architecture, and gradually upgraded to industrial innovation chain system from environment-oriented instruments.
    Finally, this study puts forward some suggestions to improve relevant policies, including optimization of supply-oriented and environment-oriented policy instruments structure for sensing platform, balanced application of environment-oriented and demand-oriented policy tools in supporting smart industries; development of data fusion, data mining and demonstration application of commercial database to foster emerging strategic industrial clusters, structured configuration procurement, collaborative incentives for innovation and entrepreneurship as well to provide strong support for high-quality development of smart city.

Key words:  smart city, policy network, evolution, policy instrument, text content analysis