With the continuous advancement of medical information technology, the widespread adoption of electronic medical records has significantly enhanced the efficiency of healthcare services. However, it also places higher demands on privacy protection, fine-grained access control, and efficient searchability of medical data during the sharing process. Therefore, ensuring data privacy while supporting multi-keyword search and fine-grained access control has become a key research issue in medical data sharing. In this paper, we propose an anonymous attribute-based multi-keyword searchable encryption scheme for medical data sharing using blockchain. Our scheme protects user privacy by concealing the access policy, ensuring the confidentiality of fine-grained access control. It also supports efficient multi-keyword search over encrypted data. Blockchain is employed as an immutable auditing mechanism to ensure the traceability and trustworthiness of the data access process. Medical data is stored in the interplanetary file system to eliminate the risk of single points of failure. Security analysis and performance evaluation demonstrate that the proposed scheme is feasible and effective, providing a reliable solution for secure medical data sharing.