The BUIDL fund launched by BlackRock is becoming a compliance cornerstone in the DeFi world. As the largest tokenized government bond product globally, BUIDL combines on-chain efficiency with the stable returns of traditional assets, creating a "permissioned DeFi" blueprint through Securitize, Circle, and others. This article delves into its operational mechanisms, technical architecture, and market impact, while exploring its reshaping of the RWA (real-world assets) sector and the long-term risks arising from philosophical divergences.