Blockchain technology is a new distributed infrastructure and computation paradigm that generates, stores, manipulates, and validates data through chain structures, consensus algorithms, and smart contracts. The new trust mechanism is built to promote the transformation of Internet technology from Internet of information to Internet of value. Since the data in the blockchain is stored and verified by means of public transaction records and multi-peer consensus confirmation, it poses a great challenge to the transaction privacy protection in the system. This study first analyzes the characteristics of the blockchain system transaction model and its differences from the traditional centralized system in identity authentication, data storage and transaction confirmation, and describes the main contents, key issues and security challenges of identity management in blockchain. Secondly, the different implementation technologies of identity management and privacy protection are analyzed in the current mainstream blockchain platform from three aspects, namely, identity identification, identity authentication, and identity hiding. Finally, the shortcoming of the existing blockchain identity management technology issummarized and the future research directionsare proposed.