Based on the concept of open complex system, the paper analyzes three causes of system complexity: system structure, combination exploding and human intervention. And then the paper pointes out that "un-repeatability" is a core characteristic of complex giant system (CGS). Applying the system dynamics to complexity research, the paper constructes a theoretic framework for studying the large scale complex system. The framework proposes the rules of assigning and co-operating the use of qualitative and quantitative analysis. And the paper studies the application of the framework to the large scale antagonism complex system.