The article argues the "dual economic structure" is a typology of China's modern economy. Due to the gigantic population and a series of institutional constraints from he society inside, this structure faced a critical population crisis. After 1949, to try to keep a balance between order and efficiency, the Chinese government coercively fragmented the unconstrained two-ways flow of capital and labour-force within the structure, to anchor the existed dual economy. A kind of "dual social ststem" was derived by this structural transformation, which should abe regarded as a stagnant option of the regime. The author also provides a normative and efficiency analysis of the dual social system under the influence of the dual economic structure, as well as its prospect and significance of reform.