Abstract: Using the estimation of kernel density method， the article focused on the data of 74 counties in Yangtze River Delta from 1991 to 2011， and estimated the per capita disposable income of urban residents and the per capita net income of rural residents by nonparametric method， and on this basis， we analyzed the evolutionary tendency and income gap of county residents in Yangtze River Delta. The results proved that both the urban and rural incomes of county residents in Yangtze River Delta increased year by year. Nevertheless， whether in urban or rural areas， the income gap between high and low earners was increasing. At the same time， the income gap between high and low earners in urban residents was significantly greater than the rural residents. In addition， the income gap between the urban and rural residents was also increasing. The polarization of income distribution and the huge income gap between urban and rural residents will become one of the important reasons hindering the economy development of the Yangtze River Delta. In consequence， its necessary to adopt some measures to slow down the polarization of income distribution and narrow the income gap between urban and rural areas.

Key words: Kernel density estimation, nonparametric estimation, income distribution density curve, urban\, rural income gap, Yangtze River Delta