Tendency analysis indicate that the yearly runoff of three typical basins (Dali river, Hailiutu river and Xiaoli river), which belong to riverhead gully section, sand and wind section and hill section respectively changed consistently in 1970, namely the annual runoff has showed decreasing tendency since 1970. Compared with the runoff in 1959~1969, the average extents of water reduction in riverhead gully section (Dali river) and hill section (Xiaoli river) are maximal, namely 36.33 % and 36.21 %, respectively, and the one of water reduction in sand and wind section (Hailiutu river) is the least, namely 20.61 %. The variation of the extents of water reduction is mostly caused by integrated results of different underlying surface status, soil and water conservation measures and controlling degree, rainfall variation in different physiognomy type areas. The monthly water balance model for calculating runoff on loess plateau has been used in analyzing the benefits of water reduction by soil and water conservation. The results indicated that the benefits of three typical basins water reduction in 1970s didnt show significant difference, but the benefits of water reduction in 1980s are very significant difference. The benefit of water reduction in hill section (Xiaoli river,24.99 %) is greater than that in sand and wind section (Hailiutu river, 17.28 %) and in riverhead gully section (Dali river, 13.13%). Results above are the basis of evaluating the effect of eco environment of the Loess Plateau on the water resources and the evolvement of water environment of Yellow River.