Analysis and study were carried out by means of mathematical statistics on sediment reduction effect by soil retaining dam with different storage capacity allocation proportion in Dali river watershed of the Yellow River. The results indicate that, sediment reduction by large, middle and small soil retaining dam account for 80.1%, 14.6%, 5.3% of the total reduction; the sediment reduction benefit has reached its maximum since 1990s, amounting to 30.2%, with corresponding storage allocation proportion of 1.84:2.37:5.79.Dam and reservoir have obvious influence on the correlation between rainfall and sediment in the river watershed, sediment transport is reduced by 10 million ton corresponding to annual average flood season rainfall of 350mm in the watershed. Within the sediment reduction capability of soil retaining dam, the sediment reduction volume increase with more rainfall in the flood season, having the feature of the more incoming sediment is, the more sediment reduction will be.

Analyzed the relationships between rainfall and warp dam block sediment in Jinghe watershed in different years by regression analysis method base on the nearest material, the date shows: (1) The respond relation is changes between the warp dam retains sand and the rain in Jinghe river basin,80's is the biggest. The critical value is 1×107 t/a;the 1d and rain season and year rain critical value is bigger than 40mm,350mm,450mm. (2) The relationships between rainfall and warp dam block sediment in Jinghe watershed were different, it had two areas include high and low block sediment base the rainfall; the high value is 3.55 times than low value. The block sediment amount of warp dam will be calculated by the corresponding relation base the actual amount of rainfall flood in watershed. (3) The warp dam retains sand amount is about 0.016t/m3 in 1 m3 flood at 80's in Jinghe river basin, the warp dam retains sand is about 0.0045t/m3 in 1 m3 flood at other years in Jinghe river basin, was growing to 0.021t/m3 near period. (4) They have the line relation between warp dams reduce sediment and soil erosion in different spatial scale river basin in middle of yellow river. The rate of reduce sediment to retain sand increase with the area decrease.