This article attempted to confirm the relationship between the exile group that occurred in the Cheonghaejin division and the change in Japan's Silla policy in the first half of the 9th century. In the first half of the 9th century, the Cheonghaejin forces, which led the trade between Silla and Japan, divided, resulting in exile. Japan, which needed the help of Shin-line for foreign exchange until the 830s, established a response system by deploying interpreters and overhauling the trade system to prepare for Shin-line's arrival. However, as Cheonghaejin was divided after Jang Bogo's death, the possibility of the exile group entering Japan was suggested, Japan's Silla policy gradually began to change. In Japan, it was intended to prevent Sinline from entering the country and to prevent exchanges between Sinline and the Japanese by excluding Silla merchants from the management trade system. In addition, military defense was strengthened on Daemado Island to prepare for invasion from Silla. These changes seem to reflect the vigilance against the entry of Cheonghaejin exile forces, which were independent military and political groups at the time. Doyle of Cheonghaejin exile forces could have caused the possibility of domestic military and political disputes due to pirated coastal looting of Cheonghaejin forces, governance confusion caused by collusion with local forces, and settlement of military groups. Therefore, the Japanese ruling class was wary of the Qinghai power's Doyle and exile, which is thought to have led to Japan's Silla policy in the mid-9th century to strengthen its exclusive military boundaries.