Abstract: Abstract:To clarify the effects of contour trenches engineering measures on soil water balance and redistribution, we took enclosed grassland as CK and assisting with artificial rainfall simulation, dynamic processes of soil water, soil moisture balance and the factors affecting the soil moisture balance in 0-100 cm soil layers of the contour trenches had been studied in typical grassland slopes of Loess Hilly Region in Ningxia. The results represented that: 1) the soil moisture dynamic in contour trenches and enclosed grassland changed seasonally with rainfall. During the period from March to December, the soil moisture of measurements showed a similar figures within 0-60 cm (P>0.05), while the figure of contour trenches was higher in 60-100 cm (P<0.05). The coefficient of variation of soil water decreased with the deepening of soil layer correspondingly, and the moisture content of contour trenches in 0-100 cm soil layer is generally higher than that of enclosed grassland. 2) Contour trenches could retain slope runoff and change soil water balance. Most of the time, soil water storage showed a negative change in contour trenches and enclosed grasslands, and during the experiment, the change of soil water was -32.53 mm and -31.20 mm respectively. Compared with enclosed grasslands, the contour trenches were greater propensity to form water deficit in the case of the little rainfall and small runoff. When the runoff was large (from July to September), water surplus in contour trenches was higher than that in enclosed grasslands, so that water increment in contour trenches was 20.68 mm higher than those in enclosed grasslands. 3) The contour trenches could supply more and deeper water supply to the soil than the enclosed grassland after intercepting slope runoff. When the runoff was 10.49 mm, the infiltration water of the enclosed grassland was 8.49% of the contour trenches; when it was more obvious with a larger runoff, and the increased moisture in the contour trenches can be reached 86.90 mm, while the infiltration moisture in the enclosed grassland after rain was only 27.13 mm. But water loss of the contour trenches was higher than those of the enclosed grassland, partly because the lateral infiltration aggravated the water loss of the contour trenches. The 0-2 hours after rain was the most intense period of soil water loss. With the passage of time, compared with contour trenches, soil moisture content in enclosed grasslands approaches the soil moisture content before rain earlier. Lack of precipitation on the Loess Plateau, Intense evapotranspiration was a major cause of soil water deficit in the enclosed grasslands and contour trenches. Finally, according to the research paper, it is necessary for us to comprehensively consider the factors such as rainfall, slope, vertical spacing and cost to set up the contour trenches in the typical steppe of the Loess Hilly Region in Ningxia.