Active-stage gully erosion processes can result in steep rise of sediment yield, thus seeking effective ways has important implications for the prevention of slope gully erosion. To quantitatively evaluate the cornstalk mulching effects on controlling soil erosion on loess hillslope with gully, a series of artificial simulated rainfall experiments were conducted to study the effects of different combinations of cornstalk mulching positions (one was whole plant buffer mulching on the head of the gully and the other was filling the gully with clipped short cornstalk) on the gully erosion on loess hillslope under the typical high intensity erosive rainfall (on the Loess Plateau) condition. The results showed that the runoff amount was reduced by 7.2%~13.8%, while the sediment yield and the average runoff sediment concentration were reduced by 8.3%~46.2% and 19.1%~49.6%, respectively. Treatment H+G (ephemeral gully head + all gully covered) and H+MG+RH (ephemeral gully head + main gully + rill head covered) got the best effect with reductions of 45.0% and 46.2% in reducing slope sediment yield, respectively. It was obvious that cornstalk mulching reduced sediment yield by changing the runoff-sediment relationship instead of reducing the runoff amount. The whole plant buffer mulching on the gully head was more effective between two mulching positions. Cornstalk mulching on different positions can reduce the channel runoff velocity, sediment transport capacity as well as runoff erosivity, which was meaningful for reducing soil erosion. For example, cornstalk buffer mulching on gully head and filling gully can both reduce the runoff velocity more than 42.6%. As a result, once gullies appeared on the loess hillslope, cornstalk mulching on active-stage gully head would be the best way to control gully erosion. Much better effects can be exhibited when gully itself was mulched with clipped short cornstalk at the same time.