Abstract: The length selection of long-wall face is directly related to the mine centralized production degree,It is not only beneficial to improve the mine production,but also to reduce the cost and achieve high yield and high efficiency.Base on the characteristics of the length selection of long-wall face,a mathematical model of working face optimum length is built.Finally,the rule of working face optimum length while the long-wall face length parameters (thickness of coal seam,shearer running rate,the wages,the cost of equipment and the supporting cost) changes is revealed.