The rotary blade is usually used as a soil-gashing tool to improve degenerated grassland in Chinese arid and semi-arid zones by breaking hardened soil layer without overturning soil. This kind of rotary blades has one sharpened side-edge only. When operating, this sharp edge can penetrate into soil to break the hardened layer. A mathematical model was developed to optimize the geometry of the blade with the goal of minimizing the torque. Experiments were conducted in a soil bin to verify the model and optimize design. Variables in this study included five different sliding cutting angles of the side-edge and three different section shapes of the blade. The Soil bin soil had similar soil textures with the grassland soil to be investigated, but there were no roots and other crop residues in the bin soil. The blade was operated at a constant speed of 0.6m/s, rotational speed of 300rpm and depth of 200mm. A torque sensor was used to measure the torque of the driving shaft. The results of mathematical model and experiment indicated that the torque requirements were significantly affected by the cutting angle of the side-edge and section shape. Test results indicated that the blade with sliding cutting angles from 46°to 51°had the lowest torque requirements. Different section shapes of blades requested significantly different torques, and optimal shape was determined.