In this paper, the characteristics of the pareto fitness function are examined. Multi-Objective Evolutionary Algorithms (MOEA) is widely used in the multi-objective design optimization. It is important to distribute the search points in the pareto-frontier in MOEA. To achieve this objective, the pareto-fittness function is often used. However, its characteristics are not clarified. Thus, it is important to clarify the characteristics of the pareto-fittness function.