Rotary tiller is a land preparing implement with great practicability, which is widely used to reduce the farming time and labor spend. The left and right wheels of tractor don’t work in the same horizontal plane in practical due to the uneven farmland. Rotary tiller and tractor are connected by the threepoint hitch, which means the rotary tiller has the same gesture as the tractor during the rotary tillage. Rotary tilling in lateral inclination gesture will not only destroy the untilled bottom of the farmland, but also affect the tillage flatness, tillage depth etc. All of this will ultimately lead to the poor rotary tilling quality and low working efficiency. To decrease the influence of rotary tiller working in lateral inclination gesture, a rotary tiller auto leveling system was designed which mainly including rotary tiller, leveling rack, hydraulic control system and the auto leveling control system. The front of leveling rack was connected to the tractor threepoint hitch while rotary tiller was hanged in the lower back of the leveling rack with two pin rolls. One end of the leveling cylinder was hinged with leveling rack while the other was hinged with the rotary tiller. Therotary tiller rotated relatively to the telescopic movement of the leveling cylinder. Auto leveling control system controlled the solenoid directional valve according to roll angle of the tractor detected by angle sensor, and drove leveling cylinder stretching out and drawing back to adjust the angle between the rotary tiller and leveling rack (namely the angle between the rotary tiller and tractor). An auto leveling closecycle control was designed to keep rotary tiller working in a desired angle by the means of combining the leveling cylinder elongation detected by the linear displacement sensor and the geometrical relationship between rotary tiller and leveling rack. Experiment was taken in ridge vegetable lands between auto leveling rotary tiller and the nonleveling rotary tiller. The data of the surface flatness of the field before and after plowing was collected by the level gauge, while the tractor roll angle and rotary tiller leaning angle were collected respectively by two attitude sensors at the same time. The tillage flatness and tillage depth of two kinds of rotary tillers and the performance of auto leveling system were analyzed. Experimental results show that the surface flatness by the auto leveling rotary tiller was improved significantly comparing to the nonleveling rotary tiller, the maximum height difference of the auto leveling rotary tiller in lateral direction was 1.9cm, while the nonleveling rotary tiller was 9.8cm; the tillage depth of auto leveling rotary tiller in lateral direction was more stable, the maximum height difference in lateral direction of the tillage depth was 1.8cm, while the nonleveling rotary tiller was 9.7cm.