With the rapid advancement of smart city construction, data has become a core element of urban development. However, traditional data management models face numerous challenges in ensuring data security and promoting data sharing. Blockchain technology, with its decentralized, tamper-proof, and traceable characteristics, provides a new approach to address data security and sharing issues in smart cities. This article elaborates on the principles and features of blockchain technology, deeply analyzes the current status and dilemmas of data management in smart cities, and focuses on exploring specific schemes for constructing a data security and sharing mechanism based on blockchain technology. The article also demonstrates the application effects through practical cases and concludes with an outlook on the technology’s application prospects in smart cities, aiming to provide theoretical support and practical reference for promoting the healthy development of smart cities.