Building a good supply network has a competitive advantage in every part of business. However, people rarely know the principles from which supply chain with complex organizational structure and function arise and develop. In this paper, we develop an evolving supply network model by using complex network theory. We mainly consider three kinds of firms＇ behaviors： entering of new firms, adding new relationships and rewiring of relationships among firms. By analyzing the statistical characteristics of the evolutionary dynamics of supply network, we find that the degree distribution follows a power-law distribution. Therefore, a supply network is a scale-free network where few but significant firms have lots of connections （called ＂hub＂ or core firm）, while most firms have few connections. These results are consistent with the results in empirical researches, which will be very useful for designing a robust and effective supply network.
