The purpose of this study is that it is made clear the construction method of Japanese Castle Architecture in Korea as I study the construction method of Suncheon-Japanese Castle(順天倭城) in those days of Jeong-yu Japanese Invasion. Moreover, I intend to analyze the similarity and the difference between Suncheon-Japanese Castle and Korean Castle Architecture by a comparative study. The result of the study is showed that Suncheon-Japanese Castle seemed to be built with the object of a long time stay rather than it was of strategic importance for the national defense. In addition, it was different from other Japanese Castle in Korea because the watch tower(天守閣) of it stood in the middle of stronghold and the watch tower stronghold dividing the round of it while that of it stood the comer of stronghold. The face stone used in important part of watch tower, gate, and so on was mostly a trimed hexangular stone. On the other hand, the face abbuting on the Gulf of kwang-yang was made of naturally wild face stone. The stone cleared traces of Si-hyeol(矢穴) and domestic Castle in Japan was also made of this method after Im-Jin Japanese Invasion. According to the construction method, the wall of castle made use of the Netak(內托) method except the gate, the support stronghold and the watch. The early mountain castle in Korea have this construction method in common.