Driven by China's carbon peaking and carbon neutralization goals as well as the strategic development of deep-offshore energy resources, energy island clusters in the South China Sea are evolving from single energy-supply nodes into integrated engineering platforms that combine multi-energy coupling, energy conversion, operational support, emergency response, and long-distance replenishment. However, the existing support model dominated by nearshore home ports is constrained by long offshore distances, complex sea conditions, extended replenishment chains, and insufficient multi-stakeholder coordination, making it difficult to support large-scale and continuous operation of deep-offshore energy island clusters. This study reviews operational support models for energy islands and offshore energy hubs in China and abroad, analyzes the capability basis and limitations of ports, island‒reef nodes, and frontier facilities in the South China Sea, and proposes a three-tier coordinated support system consisting of core home ports, relay hubs, and frontier support nodes. Based on support distance, water depth, task attributes, and response requirements, the proposed system divides the support space into a nearshore support layer, an offshore relay layer, and a deep-offshore frontier layer, corresponding respectively to integrated coordination, relay transfer, and near-field response functions. Scenario-based calculations indicate that the proposed system can reduce the response time for urgent spare-parts replenishment from approximately 51.5 h to 17.5 h, a decrease of about 66%, and reduce the arrival time for medical rescue from approximately 3.28 h to 1.43 h, a decrease of about 56.4%. Institutionally, this study recommends establishing the South China Sea Deep Blue Economic Comprehensive Pilot Zone as a coordination platform, while advancing standard sea-unit certification, three-dimensional layered sea-use rights, enclave-economy cooperation, and sea‒air emergency coordination mechanisms. The results indicate that the three-tier coordinated support system can improve the operational efficiency, emergency response capability, and system resilience of energy island clusters in the South China Sea, providing a reference for the construction of deep-offshore energy engineering support systems in China.