Under the nowadays changing environment, the disasters of rainstorm flood show increasing trend, however, due to the scarcity of observational data and the complexity of hydrological processes, revealing hydrologic response mechanisms have become one of the key and difficult issues in geography, hydrology, and so on. Based on two closed drainage basins in the Yangtze River Delta, comparative field observation experiments were carried out to explore the hydrological response and the mechanism of runoff generation under different land use/cover conditions. The results show that the seasonal variation of soil moisture content in the long time series due to the humid climate in the Yangtze River Delta region. The deviation coefficient of soil moisture content is larger in surface layer and flood season, but lower in deep layer and non-flood season. The soil moisture content in the longitudinal profile of bayberry forest increased gradually from surface to bottom layer, while the trend was opposite for cultivated land and bamboo forest. From surface to deep layer, soil moisture content of hillslope, urban land and wasteland showed reverse S -, W - and V - shaped fluctuation trend in the longitudinal profile. There is a strong correlation between flood characteristics and total rainfall, with R_² > 0.49 and p < 0.01, indicating the dominant role of runoff generation under saturated condition. Moreover, the flood characteristics are mainly influenced by the physical geographical characteristics and rainfall, while the antecedent conditions have relatively little influence in humid region. The increase of water level and unit rainfall water level in Yinjiang experimental basin with a higher impervious water level ratio were higher than that in Xilongxi experimental basin, which indicates that the expansion of impervious water surface in urbanization area may lead to the decrease of rainfall infiltration and the increase of runoff coefficient, and thus leading to the rise of flood peak.