Abstract: Taking the large section open-off cut of 3101 working face in one mining area of Daxi Coal Industry as research object, on the basis of analyzing the physical and mechanical properties of the roof rock, the support technology of the large section open-off cut was designed by used of theoretical arithmetic and engineering analogy. The supporting effect was monitored by the dynamic monitoring system of roof separation. The result is that the 6 groups measuring points of the surrounding rock are less than 40 mm and the displacement is within the permissible range. The support can resolve the support of the large section open-off cut.