Climate change is one of the main reasons of water resources decrease and ecological deterioration in the Yellow River basin in recent years. The WEP - L distributed hydrological model was applied in this paper to analyze the influence of climate change on water resources (luring the past fifty years, and analyze the response of water resources to the main climate factors such as precipitation and air temperature it) the headwater area of the Yellow River basin and the sub - basin of Yiluo river, a tributary in middle reaches of the Yellow River as studied area. The results demonstrated that under the impacts of climate change, the change of water resource from 1980 to 2000 compared with that from 1956 to 1979 were as follows: surface water resources decreased 3.03 billion m(3), groundwater resources decreased 2.50 billion m(3) with 380 million in decrease of the groundwater non - overlapped with surface water, and the total water resources decreased 3.42 billion m(3). With increase of air temperature, the total water resources decreased with the decrease of surface water resources and groundwater, and the groundwater non - overlapped with surface water changed little. The tendency of total water resources and its composition was the same as change of precipitation. The responses of monthly runoff to air temperature varied with seasons. The responses of monthly runoff to precipitation change could be divided into three phases, the dry season phase, the wet season phase, and the transitionary season phase.