Supply chains are complicated dynamical systems due to many factors, e.g. the competition between companies, the globalization, demand fluctuations, sales forecasting. Hence, they must react to changes in order to adapt quickly its network. In this paper we focus on a two echelon supply chain problem dealing with supplier selection issue during periods in a highly flexible context. How to select suppliers is the main question we try to answer in this research. A suggested approach based on dynamic optimization is highlighted to solve this problem.