The widespread adoption of emerging technologies in healthcare has led to an exponential increase in medical data generation. However, the security of healthcare data has not kept pace, with frequent breaches and unauthorized access posing substantial threats to patient privacy and the integrity of healthcare systems. Although existing access control frameworks offer partial solutions for secure data access, they fall short in authorization granularity, privacy preservation, and large-scale, high-frequency access. To bridge these critical gaps, we propose a novel role-based access control (RBAC) framework that enables secure and efficient management of large-scale, high-frequency data access. The framework first introduces a real-time access behavior analysis algorithm. It then integrates Ethereum smart contract technology with the RBAC model to construct high-performance, scalable access control contracts. Subsequently, the framework simulates the EMR interaction process in a representative healthcare scenario. Through rigorous security evaluations and experimental simulations, we demonstrate that the proposed framework enables robust accessor management, secure data sharing, and effective support for large-scale, high-frequency access while maintaining operational efficiency. This work offers a scalable and practical solution to healthcare data security in the era of big data and population aging.