Abstract: Due to its decentralized and traceable nature, blockchain has been widely used in various fields such as digital currency, supply chain finance, and smart healthcare. As the demand for applications continues to expand, the need for independent blockchains to collaborate to build a broader value Internet is increasing, making it urgent to study cross-chain technology. However, as blockchain develops towards the application chain model, the number of blockchains has greatly increased, and the scale of cross-chain interaction has also increased. Existing cross-chain research cannot meet the challenges in terms of architectural scalability and cross-chain requirements diversity. Therefore, featured by the idea of “on-demand domain”, we propose an on-demand and scalable cross-chain architecture called PieBridge and raise a four-layer cross-chain interaction protocol stack. By decoupling cross-chain transmission, verification, transactions and applications, our protocol stack meets the diverse requirements of cross-chain applications in terms of privacy, security, and performance. We implement the PieBridge prototype system and further verify PieBridge’s scalability and flexible support for diverse cross-chain interactions from both theoretical and experimental perspectives.