Combined rainfall-runoff forecast system has been established by using the TOPMODEL coupled with the Sacremento routing scheme for the Han River basin. This system is composed of both the AF (AWS-Flow) and CAF (Coupled Atmosphere-Flow) forecast system. The AF forecast system, the short-term flow forecast system based on the lag from the rainfall to the streamflow at its outlet, uses the AWS rainfall as the pre-input, and the CAF system is coupled with the SRAPS's (Short Range Analysis and Prediction System based on the MM5) forecasted precipitation. We have performed the 28 forecast experiments at 6-hr interval from 03 LT 1 August 2002 by running the AF, CAF, and the control (CTRL) system forced by the observed inputs: streamflow, AWS rainfall, and dam control data. The simulated results indicate that there is not nearly difference between the AF and CAF forecasted streamflow within the 6-hr forecast lead time, but after this time the CAF gives the better results than that of AF.