The optimal fuel injector shape for a supersonic combustor is investigated in terms of rapid mixing of fuel jet and supersonic airstream. A Multi-Objective Genetic Algorithm (MOGA) has been applied to discover the optimal fuel injector shape, and two goals of the optimization are adopted. One is to maximize the jet core height, and the other is to minimize the total pressure loss. The algorithm works well, and the characteristics of the optimized shapes for the fuel injector are understood. The effects of the fuel injector shape, which is derived from the statistical process of the optimized shape, are numerically investigated on the jet core height and total pressure loss.