Loess Plateau of China is one of the most serious soil erosion areas in the world.This study was conducted to analysis hyd-dynamic mechanism of soil detachment process for original soil core in loess region under the range of f low discharge (400~ 1360L/h) and slope gradien t 10.51%~ 21%).The main conclusions are as follows: 1.Based on analyzing the variation characteristics of soil detachment capacity by rill flow in loess hill slope,the factor model of soil detachment capacity by rill flow was established.2.Based on analyzing the coupling relationships between soil detachment capacity by rill flow and hydrodynamic parameters,the response characteristics between soil detachment capacity by rill flow and different hydrodynamic parameters were revealed.3.Based on analyzing the hydrodynamic parameter correlated with soil detachment capacity by rill flow,the mechanism and dynamic model of soil detachment (soil detachment capacity) by rill flow was revealed and established.