The objective of this study is to estimate nonpoint source loading using HSPF (Hydrologic Simulation Program-Fortran) model. Hydrologic and water quality parameters of the model were calibrated using 2 years observed data (2000 - 2001) at Gyeongan gauge station. The Nash-Sutcliffe model efficiency (E²) of hydrologic simulation was 0.84, and the E² of total notrogen (TN) and total phosporous (TP) was 0.53 and 0.25 respectively. For TN, parameters of washoff potency factor POTFW, nitrification rates of ammonia at 20 ℃ (KTAM20), denitrification rates at 20 ℃ (KNO320) were sensitive. For TP, parameters of adsorption related ADPOPM(2), ADPOPM(3) were sensitive.