Abstract: Based on investigation into influence factors of geology and mining,such as stratum nature of main roof,mining depth,mining thickness,coal pillar strength and so on,combing with specified geology and mining factors,the changing principle of size of coal pillar along with mining depth,mining thickness and coal seam inclination angle etc is probed into,the size of coal pillar calculation formulas are established.In a mine,under different mining depth and thickness,coal seam inclination angles conditions,the size of protection coal pillar is not tradition holding liner relations but complicated un-liner relations.So theory basis is provided for designing coal pillar.