It is required to develop an appropriate sediment routing model for describing behavior of sedimentation in a whole river system. This research deals with a synthetic sediment routing model based on DEM (Digital Elevation Models). This kind of model has several subjects to be examined from the viewpoints on model construction such as computational time interval, tuning hydraulic parameters, effects of computational mesh scale on the results, pseudo channel network made from DEM and so on. Authors have hitherto been examined some of the subjects mentioned above in the mountainous Hayakawa River basin (509km²). In order to apply the model to larger river basin, the Fujikawa River basin (3, 571km²), a new method of automatical tracing of the channel network is adopted. In this paper, difference of channel networks between the conventional method and the new one is examined, and reasonable way of smoothing river bed as an initial situation is searched. The results of some cases of simulation on sedimentation in the basin is also discussed.