Addressing the issues of attribute privacy leakage and insufficient scalability in existing blockchain multi-domain access control models， a Cross-Chain based Multi-Domain Access Control Model （CC-MDACM） was proposed. Firstly， based on Attribute-Based Access Control （ABAC） and relay chain technology， a cross-blockchain multi-domain access control model was proposed， enabling autonomous authorization within domains and fine-grained access control across heterogeneous blockchains through the relay chain between domains. Secondly， by combining a threshold homomorphic encryption algorithm based on SM2 with zero-knowledge proof technology， a cross-blockchain multi-domain access control scheme with dual concealment of attributes and policies as well as scalability was proposed. This scheme allowed data to be verified and decrypted by distributed nodes on the relay chain and facilitated access control decisions in the ciphertext state. Attributes and policies were protected through dual concealment， and access control policies were dynamically extended. Additionally， Raft consensus was adopted to ensure the reliability of decryption. Finally， the proposed scheme was analyzed by security theoretical analysis and simulation experiments. The results demonstrate that， while ensuring dual concealment of attributes and policies and supporting dynamic expansion of access policies， the proposed scheme effectively resolves the multi-domain access control problem across heterogeneous blockchains. Compared to the Distributed Two trapdoor Public Key Cryptosystem （DT-PKC）， encryption and decryption efficiencies of the proposed scheme were improved by 34.4% and 44.9%， respectively.