Abstract: The perpendicular line method is widely used in the design of protective coal pillars for surface buildings or other structures above coal seams, but there are some unsolved problems regarding on its principle, such as the strike direction of the seam is ambiguous, which leads to the need for manual intervention, and the overestimation of the coal pillar at the corners with small angles. Aiming at the buildings of the scale of a village, the mining and loose layer parameters should be given according to the locations. Taking the coal seam dip direction as the reference orientation for the perpendicular line method instead of the unclear seam strike direction, which allows for the automatic selection of the perpendicular line equations and the calculation of the line lengths. An acute-angle optimization algorithm has been proposed to solve the problem of leaving too-large coal pillars at corners with small angle values. Based on the above improvements, the calculation of coal pillars is automated using MATLAB programming, resulting in a certain reduction in coal pillar size. The optimized perpendicular line method can be better applied to the design of protective coal pillars.