This paper tries to answer the question, "how does PRC's economic coercion affect the ROK's security policy decision?." To answer the question, this paper analyzes two cases, THAAD deployment and Joining Quad utilizing the Perspective Theory as an analytic framework. As the result of the analysis, THAAD deployment, the security policy of the first case already finished could proceed by two variables, loss frame, and high decision weight. The loss frame matters because it makes the decision matter risk-seeking while the gain frame works in vice versa. However, in the case of Joining Quad, the frame is in gain despite high decision weight considering conditions in June 2022. Thus, at this juncture, the government of ROK might be able to join Quad with a low level of Chinese backlash. This could be possible only because the PRC is seeking to avoid international backlash in the context of Western cohesion by the Russian invasion of Ukraine in 2022. Things could be different if time goes on.