The research figures out the causality between the strategy assessment and civil-military relationship in South Korea, focusing on the torpedo strike against the South Korean corvette Cheonan(2010) and the shelling of the South Korean island Yeonpyeong(2010). The strategy assessment is a process for civil and military to shape and implement the military strategy which fits most with the national goal as well as its capability, consisting of sharing the information, discussing the strategy, evaluating the corporate competence and clarifying the authorization process. Risa Brooks argues the quality of the strategy assessment is determined by the two features of civil and military relation, divergence of preference and balance of power between civil and military. The strategy assessment of South Korea before two incidents in 2010 disclosed the serious problems in the process of strategy discussion and corporate competence in strategic assessment that thwarted in deterring the local war threat from North Korea. The bad strategic assessment at that time is rooted in the balanced power between civil and military (the relative autonomy of the military) despite their convergent preference, analysed on the basis of documents and comments from high civil and military authorities. Hence, Brooks` argument on the strategic assessment and civil-military relation provides a good framework to understand and analyze the strategy of South Korea on the occasion of two strikes from North Korea.