Abstract: With the progress of information development of medical industry, the medical field has got into the era of big data. However, it still faces many challenges in data heterogeneity, interoperability, and privacy protection. In response to the above problems, a decentralized medical big data sharing model based on ring signature is constructed. The model maintains a reliable medical ledger database based on the decoupling of blockchain, ensuring that the privacy data cannot be tampered. It constructs a private data storage protocol based on ring signature, which guarantees medical data and patient identity privacy with its full anonymity. We proposed a medical information strict access control management mechanism based on smart contract automation execution of preset instructions. The authority and confidentiality of medical privacy data are guaranteed by clearly dividing the access rights of medical privacy information. The safety test results show that the model has better real-time and robustness than the traditional medical big data sharing model.