This study involves a laboratory rainfall simulation to design scale model experiments of soil erosion on the interrill. A net-styled downward-spraying rainfall simulator generated laboratory rainstorms of 1.0~4.0 mm/min with raindrop characteristics approaching those of natural rainfall and a series of test troughs containing a reconstructed tilled loess with saturated water was used to evaluate the interrill erosion. In some events of the experiments, rainstorms of known intensity and duration were applied to the test trough and the ensuring sediment-runoff water mixture was collected with results expressed as erosion quantity. In other experiments, the mixture, from each certain period, was analyzed with results expressed as sediment concentrations and runoff. As a result, sediment concentrations varied acutely as time went on though the runoff from the slope kept stable, and dry weights of sediment from the slopes were approximately proportional to a power function of rainfall intensity.