Recently in international politics, studies from various perspectives have been attempted on theories and actual cases of dipomacy in middle powers. This study comtemplated the diplomatic strategy of ASEAN, an alliance of ten Southeast Asian countries, from the perspective of Network Theory as a noticeable case of diplomacy with middle powers. The ten member states were able to expand their strengths by creating a power beyond the limits of individual nations within the network of ASEAN on the inside, and building an extensive network within the center of ASEAN on the outside. ARF, ASEAM, ASEAN+3, EAS, and RCEP are all representative bodies rooted in ASEAN. ASEAN got attention as a key actor in various regional councils and was able to leap into the world's fifth-largest economy. As such, the centrality emphasized by ASEAN while pursuing a network diplomacy strategy in both directions is also one of the core principle of Network Theory. Looking at the diplomatic strategy developed by ASEAN, it can be evaluated as implementing the centrality through the three elements emphasized in Network Theory: betweenness, closeness, and degree. In ASEAN's diplomatic strategy, the internal centrality that unites the ten member states is an essntial requirement of ASEAN's external centrality that coonects external actors. In order to broaden the foundation for common values and norms among member states and secure a stronger centrality, changes are necessary for the "ASEAN way." Meanwhile, South Korea should improve its status in ASEAN diplomacy by filling in the structural voids found in ASEAN's network, while comtemplating the direction of new middle-powered diplomacy using network strategies.