The major barriers to modeling hydrological processes in semi-arid and arid areas are a lack of understanding and model representations of the distinctive features and processes associated with runoff generation in those regions and a paucity of field data. In this study, TOPOG, developed by CSIRO in Australia, was modified by adding model representations of some of the predominant features and processes identified through field and experimental investigations on a semi-arid agricultural catchment with complex-terrain and mixed land use in the Loess Plateau of China. The modified models were then used to continuously simulate both slowly changing hydrologic states during interstorm periods and fast-responding overland and tunnel flows during stormflow periods. Finally, the effectiveness of model simulation under a wide range of rainfall and spatio-temporally varied land cover conditions was tested by comparison of simulated and observed stormflow discharges from both catchment outlet and internal plots. Considerable variability in simulation accuracy was found among storm events and within the catchment. The simulation results highlight the critical importance of crusting and some land management practices on stormflow generation and its spatial variation in this area. Overall, the simulations showed that the model represents reasonably well storm flows generated by rainfall events with recurrence intervals > 2 years, which account for more than 60% of runoff and 70% of sediment leaving this area.