The parameter calibration of TOPMODEL is influenced by digital elevation model (DEM) resolution because of the utilization of scale-dependent topographic index representing hydrologic similarity. The downscaled DEM from the coarse-resolution DEM and the resolution factor are applied to remove the DEM scale effects on the upslope area. Meanwhile, a fractal method is introduced as an approach to account for the effect of DEM resolution on slope. A significant improvement on the estimation of slope directly from the coarse-resolution data is made by applying fractal parameters that are computed from the standard deviation of elevation and the topographic complexity index in a 3 × 3 window of the DEM to account for local variability in the surface. The method to downscale the topographic index distribution is then coupled with the TOPMODEL to develop the scale-invariant TOPMODEL and is applied to perform streamflow simulation in the context of different DEM resolutions in the Zishui catchment. Results show that the calculated hydrograph based on the DEM data at 900 and 1,800 m resolution is consistent with that based on the DEM data at 100 m resolution when the same parameter set is used.