Abstract: In order to develop and use coal resources legitimately,extend the mine service life,ease tensions between recovering and tunneling and ensure the mine developing healthily and sustainably,research of improving mining limit is carried out in 6311 working face of Shanjiacun coal mine.Through analyses of geological conditions of quaternary system,the aquifer types and water body mining dynamic grade is cleared.By the way of theoretical analysis,the heights of the fractured and caved zones are calculated.The logical size of coal and rock pillar for safety is designed,which improves the mining limit for 25m and achieved good economic benefits,which provide a reference to the size of coal and rock pillar for safety under the same geological conditions.