Abstract: The economic gradient evolution is the characteristic of regional spatial polarization, and it is also a hot topic in the study of Economic Polarized Area. This paper firstly constructed the theory of economic gradient evolution according to Perroux’s “growth pole theory” and Hirshman’s “polarizing and trickling-down effect theory”, then taken the Yangtze River Delta as the empirical study area, calculated 42 cities’ economic gradient value by means of  principal component analysis (PCA) method, studied their gradient distribution and evolution characteristics from 2000 to 2015 by using the methods of regional difference coefficient, spatial autocorrelation analysis, cluster analysis, geographical regionalization and gradient-distance curve simulation The results show that the regional internal differences firstly increased and then decreased, the spatial pattern firstly gathered and then dispersed, the slope of gradient curve firstly become steeper and then slower. This polarization reversal law is not only verified the “growth pole theory” and “the polarizing and trickling-down effect theory” again, but also can be used as an important evidence to judge whether an economic polarized area has been formed.
Key words：polarized area；economic gradient; polarization reversal law; Yangtze River Delta