Eastern China has experienced rapid urbanization during the past four decades. It is necessary to understand the climate impacts of urbanization. Previous simulations with either regional climate models (RCMs) or general circulation models (GCMs) produced inconsistent and statistically insignificant urbanization effects on precipitation during the East Asian Summer Monsoon. In the studies with RCMs, reanalysis data were used as the lateral boundary conditions (LBCs) for both urban and non-urban experiments. Since the same LBCs may limit the urbanization effects, in this research, the Weather Research and Forecasting (WRF) model nested within the Global Forecast System (GFS), both of which were coupled with an urban canopy model, were used to explore urbanization effects over Eastern China. The WRF’s LBCs in the runs with/without urbanization were provided by the corresponding GFS’s runs with/without urbanization, respectively. Results showed a significant decrease of precipitation over North China, mainly due to a profound decrease in evaporation and the divergence induced by the reduced latent heating in the middle-atmosphere. Meanwhile, to the north and south of the large-scale urbanization areas, especially to the south of the Yangtze River, precipitation significantly increased due to large-scale urbanization-induced circulation change. With the same LBCs for the WRF’s runs with/without urbanization, the urbanization effects were limited only to urban and nearby areas; no significant change was found to the south of the Yangtze River, since the same LBCs hampered the effects of urbanization on large-scale circulation. In addition, this study also demonstrates that the urban fraction may be a key factor that affects the intensity of urbanization effects within the urban areas.