This study estimated average yearly watershed pollutant loading by using SWMM(Storm Water Management Model) which is one of the l1onpoint source quality models. Two sites were measured discharge and water Quality at dry period and wet period. The rainfall data is used from 1989 to 1998. During a decade, the average year watershed pollutant loading, which is SS, BOD₅, TN, TP, were 2.39E+06kg, 2.92E+05kg, 2.53E+05, 2.66E+01kg respectively. During dry period, SS, BOD₅, TN, TP loadings were 1.89E+05kg, 1.17E+05kg, 1.04E+05kg, 1.1lE+04kg, and during wet period 1.89E+05kg, 1.17E+05kg, 1.04E+05kg, 1.11E+04kg respectively so wet period loadings are more than dry day loadings.