Abstract: Land use/cover changes（LUCC） have profound impacts on many aspects of the environment,including hydrology.To control the severe soil erosion in the Loess Plateau,China,a great number of soil conservation measures and eco-environmental construction have been implemented in the studied region especially from 1970s.These measures have resulted in large scale land use/cover change and considerably modified the streamflow leading to reduced water yield.It is important to understand the impacts of the soil conservation measures on streamflow and its tempo-spatial change pattern in the arid and semi arid region.In this study,data from 38 catchments in the Hekou-Longmen section of middle reaches of Yellow River were analyzed to investigate the responses of streamflow to the land use/cover changes.The nonparametric Mann-Kendall test and Pettitt test were used to identify trends and change points in the streamflow records.It was found that 29 out of the 38 catchments had significant downward trends in annual streamflow ranging from 0.17 to 2.61 mm/a.Pioneer abrupt changes in annual streamlfow defined by change points occurred from 1970 to 1973 found in Wuding River.In other catchments,the change points occurred from 1978 to 1985,the latest was in 1994.The other catchments with no significant trend located mainly in South-West part of study area probably caused by the complex human activities.For Hekou-Longmen section,the streamflow was significant downtrend with 0.79 mm/a and the change point occurred in 1979.Frequency analysis showed that the ratio of reduction in annual streamflow during before and after periods at 5%,50% and 95% percentile were mostly from 30% to 60%.The highest reduction reached to 73.2%,63.5% and 69.7%,respectively.For the whole Hekou-Longmen section,the annual streamflow reduced by 46.5%,42.4% and 24.1%,respectively.It was estimated that the land use/cover changes accounted for over 50% of reduction in mean annual streamflow in 9 of 11 catchments.The construction of soil conservation measures,especially sediment trapping dams,appeared to be the main cause for the changes of mean annual streamflow.