Abstract: Building specific sediment yield map is important for planning of soil and water conservation. While the traditional method to build a specific sediment yield map usually ignored the scale effect on specific sediment yield, namely, the influence of drainage area on specific sediment yield, many researches have proved there is a functional relation between specific sediment yield and drainage area. Therefore, the scale effect should be considered when building specific sediment yield. In this paper, the scale effect of specific sediment yield is studied in the Haihe River Basin. Following the principles of integrity of river basin and the similarity of topography, the Haihe River Basin is divided into 9 sub-regions. The scale effects of all sub-regionson specific sediment yield could be classified into three regional trends: (1) a flat trend; (2) a decreasing trend; (3) an increasing trend. Scale effect for each sub-region is explained based on location, topology, geomorphology, and land use forms. Sub-regions with flat trends are mainly located in the areas of mountainous upper reaches and limited flood plains of lower reaches. Soil erosion is severe in mountainous area, and sediment has little chance to silt down on flood plains. Sub-regions with decreasing trends are mainly located in the areas of limited mountainous upper reaches and large flood plains of lower reaches, where sediment transported from mountains have more chance to silt down. There is only one sub-region with increasing trend, located in the upper reaches of the Baihe River Basin and extended from grassland with slightly soil erosion to the loess covered area with severe soil erosion. Equations are used to offset the influence of drainage area on specific sediment yield, and specific sediment yields of all hydro-stations are all calculated under a standard area. Kriging interpolation is used to create specific sediment yield maps on standard area of 1000 km² using equation of each sub-region. The pattern of specific sediment yield map shows strong soil erosion in the west and low erosion in the east, consistent with topographic distributions of the Haihe River Basin, with mountains in the west dominated by erosion and plains in the east dominated by deposition. There are two high specific sediment yield areas. One is located in the upper reaches of the Yongdinghe River Basin, Daqinghe River Basin, and Fuyanghe River Basin, with underlying surfacecovered by loess. The other one is located in the middle reaches of the Luanhe River Basin, expanding from loess to earth-rocky mountainous area. Those high value areas are the key areas for planning soil and water conservation.

Key words: Haihe River Basin, scale effect, spatial variation, specific sediment yield