Abstract: To understand the effects of ryegrass coverage on flow velocity at cinnamon soil slope, we analyzed the effects of five different ryegrass coverage (0,20%,40%,60%,80%,respectively) on flow velocity under the condition of artificial rainfall, conducted by two rainfall intensities(0.5,1 mm/ min) and two slopes(10?, 20?) respectively. The results showed that flow velocity had positive correlation with rainfall duration until reach the stable. Meanwhile, there were positive correlations between stable flow velocity and rainfall intensity as well as slope, while negative correlation between stable flow velocity and coverage of ryegrass grass. When the coverage of ryegrass exceeded 60%, the differences in flow velocity at different conditions declined and the influence of slope on flow velocity was insignificant. Hence, based on the threshold, we simulated the equation into two parts, given by flow velocity (V), coverage of sloping grass(C), slope () and rainfall intensity(R),when the coverage is 60%, V = 47.75(1 - C)0.27(sin)0.13 R 0.56(R2 =0.97); when the coverage is 60%, V =24.15(1 - C)0.13 (sin) -0.01 R0.49 (R2 =0.98). The correlation of the equations is significant respectively.