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Abstract. Surface water pollution has been a major problem in China. Riverside riparian buffers has been shown to be effective in reducing sediment and chemical loadings to rivers from agricultural area sources. This study was conducted to evaluate the impact on water quality by converting riverside crop fields to riparian buffer zones in the Jinghe catchment, China. Two well validated and applied models, the Agricultural Non-Point Source Pollution Model (AnnAGNPS) and the Riparian Ecosystem Management Model (REMM), were used together to conduct the evaluation. The AnnAGNPS was used to divide the Jinghe catchment into homogeneous drainage areas and generate upland loadings as inputs for the REMM, which was employed to assess the impact of riparian buffers on reducing sediments and nutrients in surface runoff from each drainage area. Five designs of the riparian buffer with different zone widths and vegetation types were tested. The standard design was following the suggestions of USDA with 20 m herbaceous perennials, 20 m harvestable deciduous upper canopy forests and 10 m non-harvestable deciduous upper canopy forests for zones 3 (next to the field), 2 (zone in the middle) and 1 (next to the river), respectively. Other designs included taking out zone 3, taking out zone 2 and further reducing the widths of the buffer zones based on the standard design. Annual totals of water inflow, sediment yields and dissolved nitrogen in surface runoff into zone 3, 2, and 1, and those out of zone 1 for the whole Jinghe catchment were calculated, compared and analyzed for all the five designs. The analysis indicated that the removal efficiency of sediments ranges from 85.7% to 90.8% and the removal efficiency of dissolved nitrogen in surface runoff ranges from 85.4% to 91.9% for all the five designs. The results of this study are anticipated helpful in guiding the land use changes in large watersheds in China for improving surface water quality by building riparian buffer zones with proper widths and vegetations.