Abstract: In order to study the support technology of large span open-off cut under the condition of compound roof in mining soft coal seam, numerical calculation, theoretical analysis, and site measurement were applied to research the deformation, displacement and failure characteristics of large span open-off cut. The surrounding rock type and support parameters were identified, and the combined support with left-hand rebar bolt, metal net, metal beam and anchor was designed. The results show that there was butterfly destruction under surrounding rock of open-off cut under no-support condition, and the roof and walls of open-off cut were critical zones of support. After supportting, the displacement of roof and walls of open-off cut reduced, the vertical stress in stress relief area of roof was obviously reduced, and the vertical stress in stress concentration area of walls increased. The range of the shear stress concentration zone formed at the vertex angle and the bottom angle of open-off cut is reduced. The results of on-site monitoring show that the support can meet the safety production and provide reference to roadway support under similar geological conditions.