Abstract: Under the background of South Korea’s deployment of ‘Terminal High Altitude Area Defense’(THAAD), this paper explores the high-reading Internet articles (with over 30,000 clicks) from unofficial wechat organizations and by so doing discusses the mass Chinese’s understanding of the East Asian geopolitics, in particular their understandings of the inter-state relations among China, the US and South Korea. Based on the content analysis and the textual analysis of these 75 articles chosen from the top-100 influential wechat organizations in China, this article has four conclusions: (1) the mass Chinese’s discussions of ‘THAAD’ firstly focus on the representations of the East Asian geopolitical patterns, and on this basis these wechat discussions construct a negative image of the Korean-US alliance; (2) the deployment of ‘THAAD’ to a notable extent ignites the Chinese people’s patriotic emotion thereby promoting the mass Chinese’s construction of the South Korean as a ‘irresponsible state’ and strengthening their disgusting emotion; (3) the South Korean and the US’s military and political activity of deploying ‘THAAD’ in the Korean Peninsula have forged the mass Chinese to know about this military system, and on this basis such representation has further strengthened the geopolitical realities that the US and the South Korean have threatened regional security and national security in East Asia; (4) taking ‘THAAD’ as an entry point, the mass Chinese pay more attention to the negative news of the South Korean and thus worsened the national image of South Korea. The negative geopolitical representations of ‘THAAD’, the US and South Korea is echoing with facts of the US and South Korea’s threats to East Asia and is echoing with the official attitude of China. Such an echo to a great extent have given pressure on the US and South Korea. Moreover, this echoing also makes the official attitude towards ‘THAAD’ and South Korea be legitimated and popularized within China. In this sense, this paper can be read as a contribution to the shortage of critical geopolitical study in China, and certainly it also has significance on the practical level.