With the development of the Information Age, the competitive dynamics in numerous industries are more intense than ever before. So, how to develop the competitive advantage and make the IT strategy in the company becomes one of the most important questions. In this paper, the implications of competitive dynamics to IT strategies are discussed. Based on the summary on the logic of various well-known IT strategy methods, particularly regarding sustainability of an advantage, an IT strategy theory incorporating competitive dynamics is proposed to predict the IT competitive advantage quantitatively. Then a recent strategy framework, Sustainability Analysis is explored.