For a given watershed that consists of urbanized areas, it was essential to predict how the runoff characteristics, such as runoff peak and volume, and travel time, change with time far planning and designing various kinds of hydraulic facilities with given recurrence interval. In this study, Mushim stream watershed was simulated using HEC-HMS model to get runoff characteristics of an urbanization basin. The results was showed that runoff was increased $1794.20{sim}2104.65;m^{3}/s$> and $1751.90{sim}1961.30;m^{3}/s$ according to the increased of rainfall and CN value recurrence interval in years. Observed storm was increased $497.91{sim}581.71;m^{3}/s$ and $506.57{sim}537.01;m^{3}/s$ for increased of CN value and impervious area. This paper is also possible to evaluate the effect of urbanization quantitatively.