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The quantitative evaluation of the characteristics of runoff and attribution identification are the basis for formulating climate change strategies and the rational utilization of water resources. The Mann-Kendall trend test, Pettitt test and Budyko framework were used to evaluate the contribution of different weather conditions and underlying surface changes on runoff during the period 1958-2014 at two stations: the watershed outlet (Zhuangtou) and the upper reach (Wuqi) of the Beiluo River Watershed on the Loess Plateau. The results showed that the annual runoff at the Wuqi and Zhuangtou stations exhibited a significant declining trend, with changing points in 2002 and 1994. Annual precipitation and potential evapotranspiration showed decreasing and increasing trends, respectively, but neither were significant. The landuse change caused by the Grain for Green Project were the main factor causing the decreased runoff in the control area of the Wuqi station, and the contribution of underlying surface changes to runoff reduction was 95.50%. Different weather conditions was the major contributor to the runoff reduction in the lower reaches of the Beiluo River, accounting for 82% of the reduction. This study can provide a scientific basis for the effective mitigation of water resource changes in this region.