With the rapid development of Internet and explosive growth of medical data,the sharing of medical data results in serious security concerns.A data security protection method based on Medical Alliance Chain (MAC) is proposed,which includes a security authentication and access control model.The query logic detached storage technology is introduced into the model to protect patients' data privacy.The storage and access of authentication credentials and access authority data are elaborated based on MAC.The security authentication and access control model based on MAC involves three roles of patients,medical staff,and the MAC.The query logic detached technology and the MAC are closely integrated to meet the needs of secure medical data sharing between different hospitals,and to protect patients' data privacy as well as the right of medical staff to access data.