The Defense strategy of Chosen dynasty in the 18th century was established by the substantial alternatives that based on historical lessons learned of Im-Jin Japanese Invasion in 1592 and Byung-Ja Manchurian Invasion in 1636. This is composed of coastal defense strategy to cope with southern threats and to do northern one. The core is further extended coastal defense concept than former days and northern defense strategy to respond to Qing dynasty cavalry tactics. This article conclusion is next. First, the origin of defense strategy at the lately Chosen is criticism about Qijiguang’s Military Tactics be based on 『Ki Hyo Shin Seo』, to seek countermeasure for its tactics. After the lately 17th century, the changes of political situation at the Qing dynasty allowed Chosen dynasty independent military reinforcement, was appeared strange vessel at western coastal area of Chosen, so that countermeasure for capital area defense system was urgent demand. Second, the defense strategy of Chosen dynasty in the 18th century extended capital and capital peripheral area, established to integrate dual defense system with whole nation fortress system. Third, declined mountain fortress service, Capital fortress, town fortress, wooden walls became important. In addition, traditional defense against Japan and Qing, these materialized capital area defense against the threat of the western coast be connected with tactical content. But, interaction between land and coast defense did not reach strategic level, yet remain fledgling phase.