Abstract: Baseflow, usually separated from total streamflow, is very important in many research fields. Two methods to analyze and calculate baseflow were introduced. The first method uses the water balance components from the soil and water assessment tool model (SWAT). The second method uses a digital recursive filter to separate baseflow from daily flow. The result was applied in Lushi basin located in the upper of Luohe to calibrate baseflow in SWAT model. Simulated flow was calibrated against calculated flow at Luohe (4 623km 2 ) from 1992～1996.To validate the model, calibrated and simulated monthly flow at Luohe from 1997～1998 was compared with a R 2 of 0.81 and an Ens of 0.84. Four sensitive factors, including CN_2 , RWVAPC, ESCO and EPCO, are determined after calibration and validation of the model. The rate of three-month (Aug. to Oct.) baseflow in annual total one is 46% because the floods usually took place in August and September in the study area. Comparing simulated monthly baseflow to the filtered one from 1992～1998, a good result can be gained with a R 2 of 0.76 and an E_ns of 0.75.The case study illuminates that SWAT model can simulate baseflow well, and the filter technique has the potential to provide realistic estimates of baseflow for input into regional groundwater models and a check for surface hydrologic models.

Key words: baseflow estimation, digital filter technique, Luohe basin, SWAT model