Abstract: River connectivity characterizes material and energy liquidities in the aquatic ecosystem of Yangtze River Delta. The assessment of river connectivity serves as the critical prerequisite for constructing ecological security pattern. In this study, a river connectivity indicator system of Yangtze River Delta was established, which consisted of 12 indicators covering three categories of physical structure, development feature and fractal topology. The kernel principal component analysis (KPCA) was introduced to interpret the nonlinear relationships among the individual connectivity indicators, and to reduce the feature dimensionality of the indicator space. An innovative river connectivity assessment framework was built on the basis of the KPCA method. The proposed assessment framework was applied to evaluate the river connectivity of the North branch basin of Jurong River, a typical small watershed in the Yangtze River Delta. The evolution feature was explored in the past five decades. The results indicated that since 1970, the deviation degree of river connectivity from the near-natural situation (1960) had kept rising to the peak in 2000 and then decreased in 2016. Four key drivers affecting the connectivity of the basin were identified as the water coverage rate, river network complexity, river network density and lacustrine surface area. The loss of tributaries could be the important occurrence mechanism on the degradation of connectivity in the North branch basin of Jurong River.