Abstract: The soil and water conservation effects of pennisetum (Pennisetum alopecuroides (Linn.) Spreng) and Arundinella (Arundinella hirta (Thunb.) C.Tanaka) grass hedges were studied under simulated rainfall and natural rainfall on fallow sloping lands (5%, 10%, 15%, 20%). The results showed that the runoff and soil loss were significant reduced by arundinella and pennisetum hedges, and the decreasing degree of pennisetum hedges was higher than that of arundinella hedges. Under natural rainfall (average rainfall intensity was 13.3 mm/h), the runoff and soil loss on plots with pennisetum hedges were decreased by 72.7% and 86.3% respectively, and on plots with arundinella hedges were decreased by 53.8% and 64.1% respectively. Under simulated rainfall (average rainfall intensity was 49.5 mm/h), the runoff and soil loss of plots with pennisetum hedges were decreased by 80.7% and 94.5% respectively, and on plots with arundinella hedges were decreased by 59.5% and 71.5% respectively. In addition, there was a negative relationship between slope gradient and corresponding soil and water conservation effects. The function of two grass hedges in preventing soil and water loss gradually decreased with the increasing of slope gradient. However, the protective functions of grass hedges could keep above 40% for runoff and 50% for soil loss. According to the results of optimal scaling regression, the presence of grass hedges had become the dominant factors followed by slope gradient and rainfall intensity in controlling soil and water loss on sloping croplands. The results can provide references for the application of grass hedges technique and protection of soil and water loss on sloping croplands in Beijing or Northern China.