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Grass roots can reinforce the strength of surface soil to withstand water flow flushing and effectively reduce soil erosion. Earthwork sites such as highways and building construction sites experience heavy soil erosion before restoration with vegetative covers. Laboratory experiments were conducted to trace the dynamic changes in soil erosion from grasses surfaces so as to quantify the effects of grasses at their establishment stage on soil erosion control, under different flow rates and slope gradients. A special device and the experimental procedures were developed for the purposes. The experimental flume consists of a flume with a sample holder at the lower end, a flow rate control valve, a water flow stabilization section and a water supply tank. Three flow rates: 2, 4, and 8 L/min, 5 slope gradients: 5, 10, 15, 20, and 25 degrees, as well as 3 surface covers: rye, Tall Fescue and bare soil (control), were used in the experiments. At early stage, short after the germination, grasses were not only too small to protect soil from erosion, but also disturbed surface soil as they broke through the surface layer of soil, which induced more severe erosion. The ryegrasses had very good erosion control capability one month after seeding while the Tall Fescue grasses needed one more month before they functioned. Other measures should be taken during the early stage of grass establishment for erosion control. Two months after the seeding, ryegrasses were able to reduce erosion by 97% while the Tall Fescue grasses reduced 78% of erosion, as compared with bare soil surface. The former is faster to be functioning on erosion control than the latter. Experimental data were used to relate soil erosion with slope gradients of different surface covers under different flow rates. The models developed were then used to estimate the effectiveness of soil erosion reductions of the surface covers as compared with that of bare surface. Changes in soil erodibilty and soil critical shear stress were estimated. Rapid reductions in soil erodibility of the grassed soil surfaces were responsible for reduction in soil erosion. The results are of values for modeling of soil erosion processes under grass-covered surfaces in the establishing period and for conservation measure implementations.