The Conestoga River watershed underwent rapidly urbanization process due to population exploding in Lancaster County of Pennsylvania during past decades. During urbanization, soil properties, surface water availability, radiation, vegetation cover and evapotranspiration are altered dramatically. The objective of this study is to investigate the effects of urbanization on hydrological characteristics in a watershed in Lancaster County, PA, which used to be covered by forest and rural area. PIHM (Penn State Integrated Hydrological Model) with the benefit of data support of HydroTerre simulates the effects of urbanization. Two scenarios of rural and urbanized watershed are simulated in PIHM respectively. Parameters in PIHM are calibrated within each land-use condition separately. Comparison of streamflow characteristics of two scenarios indicates the influences of urbanization on water balance, soil water storage, mean discharge and peak discharge of the watershed. This research is useful for urban studies and planning and flood control as well.