Tillage practices play a key role in soil and water loss control in agricultural lands. The objective of this study was to measure the soil and water loss from the tilled surfaces and analyze how slope gradient affects soil and water conservation benefit of tillage practices. All experiments were conducted in outdoor runoff plots with a size of 4 m length by 1 m width. The slope gradient was 5°, 10°, 15°, 20°, and 25°. The rainfall intensity was 1, 1.5, and 2 mm/min. We found that the runoff yields from contour ploughing, deep hoeing, and shallow hoeing were decreased by 38.19%, 32.25%, and 15.84%, respectively, compared with the smooth surface; the decrease level of sediment yields was more than 50% in three tillage measurements compared with the SS. It was suggested that tillage practices had a significant benefit in soil and water loss control in agricultural lands, but depended on slope gradient. On the tilled surfaces, the difference in runoff yields between small and large slope gradient was not significant; sediment yield increased sharply with increasing slope gradient when slope gradient ranged from 10° to 25°. The soil conservation benefit of contour ploughing, deep hoeing, and shallow hoeing was decreased by 3.08%, 4.74%, and 7.61% for each gradient rise in slope when the slope gradient was more than 15°. Regression analysis showed that the change in sediment yield with slope steepness and rainfall intensity for all treatments could be described by the exponential function. Therefore, the benefits of soil and water conservation of tillage practices changed with the increasing slope gradient, but to different ways and extents. The results provide a mechanistic understanding of how slope gradient affects soil and water conservation benefit of tillage practices in agricultural lands.