Based on water resources investigating and evaluating for the Yellow River Basin,this paper analyzed the change characteristics of the water resources since 1956,on which the change reasons were studied.The research results showed that the water resources especially the natural runoff have appeared a decreasing trend under the condition without large change of precipitation since 1990.This situation was more outstanding in the last five years.According to analysis,the decrease of natural and fact inflow in the river wasresulted from climate changing and the human activities.Based on the change characteristics,this paper also put forward the water resources quantity that can serve for future water resources planning under the condition of underlying surface.