Social， cultural， judicial， and other factors constitute the historical background of Japan’s personal information protection legislation. Its personal information protection is achieved on the basis of review and oversight safeguard mechanisms and legal protection mechanisms， while consistently balancing the dual demands of personal information protection as well as circulation and utilization throughout the evolution of the legal system， thereby continuously promoting social progress and economic development. The rapid development trends of artificial intelligence， frontend technologies， and other technologies give rise to the collection， storage， and use of a large amount of sensitive and private information data， making the protection of personal privacy and personal information even more critical. Drawing on the legal practice of personal medical information leakage cases in Japan， this paper conducted a legal analysis based on the guidance documents regarding these cases issued by the Personal Information Protection Commission， Japan. Within the basic framework of Japan’s personal information protection， it summarized the practices in the medical field regarding aspects such as the protection model in the medical field under the dual-layer legal system， the protection mechanisms for medical information， and balancing the relationship between medical big data and personal information. These aimed to offer certain references for constructing China’s legal system， improving relevant supporting institutions， and enhancing legal governance efficiency.