With the development of the Internet, optimizing routing in cross-domain application scenarios has become a significant challenge, particularly in ensuring inter-domain routing optimization without compromising intra-domain privacy in collusion scenarios. To address these challenges, we propose Blockchain-Enhanced Privacy-Preserving Inter-domain Routing, PIRchain. PIRchain integrates blockchain with Border Gateway Protocol (BGP) to collaboratively transmit routing information across autonomous systems (ASes). This approach employs secure comparison algorithms tailored to various privacy exposure scenarios, enabling privacy-preserving optimization without disclosing internal domain metrics. This approach tackles the privacy, scalability, and trust issues present in existing methods. It also mitigates privacy concerns related to blockchain transparency by encrypting and partitioning sensitive data. Furthermore, the multi-channel architecture of PIRchain enhances data isolation, ensuring high availability and resilience for inter-domain routing processes. PIRchain provides robust privacy protection under a semi-honest model with collusion, offering an advanced level of privacy in comparison to existing solutions. Simulation experiments conducted in both full and incremental deployment scenarios show PIRchain’s effectiveness in significantly reducing routing metrics. PIRchain presents a scalable solution that effectively balances privacy preservation with routing optimization.