Electronic health records (EHRs) have fundamentally transformed healthcare services by digitizing patient data, enabling rapid access to critical information and cross-domain sharing. The identity authentication scheme provides a trusted foundation for secure cross-domain interaction of EHRs. However, existing identity authentication schemes face several issues, including the reliance on trusted third parties, privacy breaches, and lack of interoperability. To address these challenges, a healthcare-oriented blockchain-assisted cross-domain authentication model (HBCA) is presented. The proposed model incorporates distributed key generation, threshold signature algorithms, and blockchain to achieve decentralized identity management. A distributed authentication mechanism enables collaborative identity verification while eliminating reliance on centralized authorities. To enhance resilience in multi-institution medical collaborations, a dynamic node management mechanism is introduced to address trust fluctuations and insider threats. A session key negotiation mechanism based on elliptic curve cryptography and zero-knowledge proofs is proposed to protect EHR transmission from replay and man-in-the-middle attacks. Security analysis demonstrates that HBCA can effectively defend against common attacks such as identity forgery and collusion attacks. Performance evaluations confirm that the proposed model achieves reduced authentication latency and communication overhead while maintaining high security and integrity in scenarios of cross-domain EHR sharing.