Baseflow is an important component of river flow,especially in the arid loess hilly and gully region.It accounts for a large proportion of total runoff and provide additional flow supply to the rivers during the dry seasons.Therefore,the research of baseflow characteristics and its impact factors in this area could contribute to more reasonable water regulations and more efficient uses of water resources.In this paper,digital filtering method was used to separate the baseflow of Caijiachuan basin from 2006to 2008.By calculating the baseflow index (BFI),controlling factors including precipitation events,land use,vegetation cover and terrain characteristics of the basin were analyzed.The results show that annual BFI averages ranged from 0.68 to 0.82.BFIs decreased with increase of precipitation.Agricultural land,scrub and plantation had negative effects on the base flow.BFIs had a linear relationship with rainfall amounts(P),river networks densities (D)and river gradients(S).The regression analysis provides a basis to analyze the characteristics of baseflow in ungauged area.