An efficient multi-objective optimization method is proposed for node-based spacecraft radiator design. In contrast to a conventional manual approach to node-based radiator design with a thermal model, the proposed approach finds an optimum design solution for radiator node combinations through an optimization algorithm. The important parameters of radiator design are radiator size and topology, represented by discrete binary design variables allocated to each node division in the candidate radiator region. The optimization problem is formulated as a multi-objective problem with two or more objectives to minimize the number of radiator nodes and temperature margins of unit boxes, and a genetic algorithm suitable for multi-objective optimization is used. A small thermal model (verification thermal model) was developed to verify the proposed multi-objective optimization of the node-based spacecraft radiator design method, and test problems for this thermal model were defined. The numerical optimal solutions for test problems show good agreement with the analytic optimal solutions. Therefore, the applicability and feasibility of the multi-objective optimization of node-based spacecraft radiator design method to practical radiator design were confirmed.