Regional disparity and unbalanced spatial distribution is the core issue in geography, the marginalization of unbalanced spatial economy development is due to spatial polarization and spatial marginalization. In order to deconstruct the marginal mechanism of marginal region, a theoretic analysis framework which includes four forces, four effects and four measure components is set up, and an empirical analysis on rural per capital net income is made. Firstly, the natural environment and irrigation condition are the main reasons of the internal marginalization of marginal region. Secondly, the development of marginal region is blocked by internal marginal force with irreversible rigid feature, because of the double restrict of natural and weak economic environment. Thirdly, external marginalization is the main reason that widens the gap of peasant's income between marginal region and developed region. Finally, under the background of economic globalization, economic transition and economic polarization of multi-level city, there are big differences of the develop environment and developing condition of nonfarm economy between different regions, thus presents the feature of persistent and strong gradient difference and marginalization of spatial economy in China. Furthermore, the future research issues and directions in this field are addressed.