Web3 is a revolutionary Internet paradigm that focusing decentralization, user empowerment, and intelligence. One of its key technologies is decentralized identity (DID), which has gained significant attention recently. However, existing DID solutions are not scalable enough to be compatible with the large-scale identity node applications required by Web3 across various fields. To overcome this challenge, we propose the first multi-layer Web3 DID architecture utilizing sharding blockchain, which provides management, scalability, and compatibility. This architecture leverages leader shards and the main chain to establish trust, while regular shards manage DID-related transactions. Specific system processes and query optimizations are also given. Besides, formal security analysis and comprehensive simulation evaluations have demonstrated that the architecture can achieve all proposed security and performance goals, including low latency of down to 2 seconds and high throughput of up to 90KTPS.