An object-orient, watershed runoff model was formulated using the SCS curve number method and routing routines, The four objects included in the model were rainfall, hydrologic unit, reservoir, and channel. Each object considers the data and simulation method to depict the runoff processes, the details of which were presented and discusses in the paper. The resulting model was applied to tile HS#3 watershed of tile Balan Watershed Project, which is 412.5 ha in size and relatively steep in landscape. The simulated runoff hydro graphs from the model were close to the observed data.