This paper reviews the state of the art in blockchain-based access control research. In the digital era, data security and access management are increasingly important. Traditional access control (e.g. RBAC, ABAC, CapBAC) faces various challenges in IoT, such as the risk of centralization and the threat of data leakage. To address these issues blockchain technology (with its properties such as distributed and tamper-proof) provides innovative solutions. This paper first introduces the three main-stream access control in IoT, then discusses the basic concepts of blockchain (including consensus mechanism, smart contract and cryptography), and analyzes the blockchain in access control applications (including authentication, privilege management and audit trail). It then discusses the advantages and challenges of block-chain access control and future research directions. Finally, the potential of block-chain in access control is summarized, emphasizing its importance for data security and privacy protection. Through this overview paper, readers can better understand the application of blockchain technology in access control and provide valuable insights for future research and practice.