Abstract: The influences of urbanization on hydrological regimes in a smarr watershed and their research approaches are reviewed. Based on the data from field observations and laboratorial modelling experiments, an index reflecting hydrologic effects due to urbanization is proposed, that is, the influences of urbanization are considered to be substantial if the impermeable area is over 20% of total catchment area. Also, the estimating method for storm floods in an small watershed due to urbanization is introduced.