With the rapid development of urbanization, the river network morphology in the plain area is harder to describe, not to mention the difficulty in quantifying the spatial influence of urbanization. Based on the data of river network in the 1980s and 2010s obtained by topographic map and the data of LUCC from remote sensing images, this paper quantitatively reveals the impact of urbanization on the river network since 1980s in the Hangzhou-Jiaxing-Huzhou area of Taihu Lake Plain with the application of multifractal theory and geographically weighted regression model. The results show that: (1) both the density and water surface ratio of river network present a decreasing trend, and their attenuation rates are 10% and 13%, respectively. From the multifractal perspective, the distribution of the river network was concentrated and the uniformity was decreased. Besides, the river sinuosity decreased by 0.5%, and the main river area length ratio increased significantly in the moderately and highly urbanized areas. (2) The response of river network evolution to urbanization has obvious heterogeneity in space. The lower the urbanization level is, the greater the evolution of river network morphology is, and the more obvious the irregularity of spatial distribution is. (3) There are four different types of urbanization level transformation in Hangzhou-Jiaxing-Huzhou region: low-low, low-moderate, low-high, and moderate-high. When the urbanization level does not change, the spatial distribution uniformity decreases, the river network morphology changes greatly and the attenuation of water surface ratio is greater. Furthermore, the greater the transformation is, the more obvious the homogenization trend of river network distribution is. Due to the effects of policy, only river network density changes significantly in the moderate-high development area. This study will provide scientific support for the sustainable development of ecological environment, so as to protect the river network.