This study proposes a trusted blockchain-based electronic evidence preservation system to enhance data integrity, security, and traceability in the agricultural supply chain. The system employs a B+ Tree retrieval and indexing mechanism to optimize on-chain data storage, improving retrieval efficiency and reducing storage overhead. An Attribute-Based Access Control (ABAC) model is integrated to enforce fine-grained access control, ensuring robust data security. Additionally, a structured transaction and data recording workflow is designed to guarantee the immutability and authenticity of preserved evidence. Performance evaluations, including the Transaction Throughput (TPS) Test and Data Storage Optimization Test, demonstrate the system’s high throughput capacity and efficient storage management, significantly enhancing query performance while minimizing computational and storage costs. The results confirm that the proposed system effectively strengthens data authenticity, security, and retrieval efficiency, offering a reliable and scalable solution for electronic evidence preservation in agricultural supply chains. Future research will focus on enhancing system scalability and integrating AI-driven traceability mechanisms to further improve adaptability and intelligence.