With the widespread adoption of medical data cloud storage, ensuring data integrity and traceability has become a key challenge. In the medical field, data tracing function is crucial for medical record tracking and compliance auditing. However, existing solutions that support data backtracking, such as CLPDP-MCMS, have security vulnerabilities and are difficult to effectively resist malicious attacks. Therefore, this article proposes a backtracking attack model to reveal the potential security risks of existing solutions, and improves the backtracking mechanism of CLPDP-MCMS based on this. By optimizing the data structure and verification protocol, the immutability of the backtracking process is ensured. Security analysis shows that the improved solution can effectively resist backtracking attacks and provide more reliable data security for medical cloud storage.