The Decentralized Identity (DID) method in blockchain enables users to manage their own data, addressing issues like centralization, single points of failure, and privacy leakage in traditional identity authentication. However, challenges remain, as mainstream Verifiable Credentials (VCs) may expose irrelevant user data during verification, while Verifiable Presentations (VPs) provide limited attribute verification without offering fine-grained control over the disclosed information. To address these challenges, we propose a Selectable Attributes Zero-Knowledge Proof (sa-ZKP) scheme based on DID and zk-SNARK. This scheme matches user-provided signed VCs with verifier-specified attributes and verifies input authenticity through digital signatures. The sa-ZKP enables users to selectively disclose attributes, achieving fine-grained privacy protection. Additionally, the Self-Sovereign Credential (SSC) algorithm allows users to prove specific attributes (e.g., age or qualifications) without revealing unrelated data. Security analysis and experiments demonstrate that the proposed scheme ensures efficient proof generation with minimal computational overhead, enabling accurate identity verification and robust privacy protection.