Runoff generation on a small semi-arid agricultural catchment with mixed land use in the Loess Plateau of China was monitored over a 19-year period. To investigate the possible spatial variations in runoff generation on the catchment, eight plots were set up on various sections of the hillslope and monitored for 6 years. Only a small proportion of rainfall events generated runoff, contrary to the assumption that rainstorms in this area are characterized by high intensity and short duration, and thereby lead to runoff generation. Runoff occurrence and yields were also found to be highly variable within the catchment. To explore further the results obtained from the field observations, portable and downspraying sprinklers were used in field experiments. Both produce similar rainfall intensities but the raindrops from the portable sprinkler have very low kinetic energy and do not break down aggregates and form crusting, while raindrops produced by the downspraying sprinkler have similar characteristics to natural rainfall. A comparison of the experimental results obtained by those two kinds of sprinklers clearly demonstrated that runoff generation in this area is largely affected by surface crusting. The effects on runoff generation of the crusts formed during previous storms and the present storm were examined experimentally. Finally, the impacts of cultivation and plowing on runoff generation were determined through field investigation and experiments. This study suggests that there is considerable potential to reduce runoff and erosion, and to increase soil moisture and crop yields on the Loess Plateau through changes of currently inappropriate land use and the improvement of land management.