In this paper, we propose a secure and efficient cross-domain authentication scheme based on knowledge graph and attribute-based encryption (ABE). Traditional ABE schemes often suffer from limitations such as rigid attribute space structures, overly complex access policies, and insufficient anomaly detection mechanisms. To address these challenges, our approach leverages knowledge graph technology to dynamically construct and optimize attribute spaces, enabling more flexible and scalable access control. Furthermore, we introduce an access policy optimization algorithm that significantly reduces computational and storage overhead while maintaining fine-grained security. Experimental evaluations demonstrate that our scheme outperforms existing methods in key performance metrics, including relationship extraction accuracy and encryption/decryption efficiency. Moreover, the integration of a countermeasure module enhances system security by detecting and mitigating potential threats in real time. The proposed solution not only improves the practicality of ABE in cross-domain environments but also provides a robust framework for secure data sharing in distributed systems, such as IoT and cloud computing.