Blockchain-based distributed ledger aims to provide consistent and tamper-resistant transaction records by integrating various security technologies such as asymmetric cryptosystem, P2P network, consensus algorithm, and smart contract. However, as each node in the blockchain system shares a copy of the public ledger, such data sharing mechanism also introduces vulnerabilities that hackers could exploit to attack private information. Privacy protection of blockchain systems thus gains wide attentions from researchers. Various techniques have been proposed to protect users’ identity, address, and transaction information from security threats. This study investigates blockchain privacy threats. It made a comprehensive survey of state-of-the-art privacy protection technologies which are categorized into three mechanisms including address confusion, information hiding, and channel isolation. The paper introduces the principles, models, and various implementations of each mechanism. It finally discusses the challenges of performance and scalability in practice and future technology advancement directions.