Abstract: In order to solve the high roof subsidence and serious sides shrinkage problems occurred in the excavation process of the large cross section open-off cut, the method combined with theoretical analysis and field observation is applied to study the pressure-relief reducing span, roof Control and stress loss compensation support in Large Section Open-off Cut, determining construction technology by secondary cutting stone and secondary acid support, and identifying the construction effect. The result shows that the surface displacement of small section is minor, and secondary side slope extension increase obviously, the relationship is 174mm by roof and the displacement is 322mm by sides, which the large section open-off cut tend to stable in 45 days, and enable control surrounding rock deformation.