The comparative study of the diplomatic character of Vietnam and Korea in the feudal era is a new research direction that is necessary to deepen diplomatic relations between the two countries in history. If modern history of Vietnam and Korea is the history of relations with the West, then in the pre-modern period, it is the history of the relationship with China. In this article, by the comparative method and interdisciplinary approach, the author points out the basic similarities in diplomacy between Vietnam and Korea in this period, for example: The two countries are in the same area of Chinese characters culture, same conjunction ("vassals" of the world order taking China as center) and basically the same diplomatic behavior with China despite flexibility through beseech investiture, tribute, presents, but the two countries strived to assert their independence in relation to China. In addition, the author also pointed out that: the position and hierarchy of Vietnam and South Korea in the "tributary system" centered on China is not the same and the degree of tolerance, patience, humility outside of Vietnam is somewhat darker than Korea. Based on geo-political and geo-cultural characteristics, the author has also started to trace the roots of these similarities and differences.