Based on the fact that corn circulation layer affects the grading performance in the working process of the hammer mill, piecewise arc-shaped screens were designed for substituting the circular-shaped screen. In order to improve the grading performance of hammer mill, the space between the hammer and screen was changed repeatedly, and the corn circulation layer was destroyed. 15 kinds of piecewise arc-shaped screens were designed for the 4KB hammer mill. The experimental study indicated that the hammer mill with the screen piecewise arc radius of 76mm and the space between arcs of 97mm had the highest production efficiency. Compared with flat circular-shaped screen, the production efficiency and power output in every kW·h increased by 29.8% and 26.6%, respectively. The over grading phenomenon was improved. Particle size of the corn was uniform and the temperature rise of the corn was decreased. 