<p>The rapid development of the healthcare industry has generated a large volume of electronic medical record data, which is stored across various hospitals. However, due to the sensitivity of medical data, it is prone to privacy breaches. Traditional ciphertext-policy attribute-based encryption schemes face several challenges, including excessive storage overhead for encrypted medical data, public access control policies, difficulties in data sharing between different hospitals, and the inability of patients to control the usage of their medical records. To address these issues, this paper proposes a blockchain-based attribute encryption access control model with constant-size ciphertext and hidden policy (ABE-BC-CSCHP). Firstly, by using an AND gate access structure based on multivalued attributes and wildcards, the model achieves a constant ciphertext size, thereby reducing both blockchain storage overhead and the computational cost of encryption and decryption. Secondly, medical data are stored in a hybrid on-chain and off-chain manner: encrypted medical data is stored off-chain in a distributed file storage system, while keyword index ciphertexts are stored on-chain. The access policies are embedded within the index ciphertext components to achieve policy hiding. Lastly, the model allows users to securely and accurately search encrypted medical data on the blockchain using a searchable encryption algorithm. To avoid single points of failure and to provide patients with flexible control over the usage of their data, the model designs multiple attribute authorities and allows patients to customize access policies. Finally, the security analysis and performance analysis compared with the current existing research shows that the model proposed in this paper is effective.</p>