A outstanding issues in the management of Loess Plateau, the fragile ecological hydraulic erosion area, is that many silt dams were rapid abandonment or the dam land couldn't be formed because of the abundance or scarcity of sediment resulted from the uncoordinated arrangement of vegetation, terraced fields and silt dams. By constructing a 3D solid model of vegetation-terraced field-silt dam-small watershed of rainfall-runoff erosion, the coordinated relationships of water and sediment were studied under different terraced fields, vegetation coverage and rainstorm levels. The some calculation equations were obtained and vertified for the sedimentation drop ratio and relative sedimentation morphology parameters of silt dams with the spatial variation of terraced fields. It was found that the relative siltation morphological parameters (C-Rt similar to a) of silt dams before and after watershed control had a good relationship with silt dam silt blocking modulus (M-s), and could reflect the coordinated relationship between vegetation-terraced fields and silt dams. When M-s <= 1000 t/(km(2) a), C-Rt similar to a and M-s is a power function relationship, which reflected that the terraces were arranged in the upper reaches of the watershed, the siltation of the silt dam was small and the siltation morphology was similar to belt or delta sedimentation. When M-s > 1000 t/(km(2) a), the C-Rt similar to a was close to the constant, indicating that the sedimentation was serious and the morphology was similar to that of vertebral body. M-s = 1000 t/(km(2 )a) is the turning point of siltation morphological parameters and erosion modulus, and it is also the allowable value of erosion modulus for current control in the Loess Plateau basin. This study is of great significance for building a water-sediment coordination relationship between vegetation-terraced field-silt dam and effectively controlling soil erosion of the fragile ecological areas in the world.