Abstract: In order to solve large span open-off excavation and support problems in three soft coal seam mine, according to the structural characteristics of roof, mechanical characteristics and stability of the main factors, we built a limit span roof strata mechanical model and obtained limit span roof calculation formula. At the same time, on the basis of studying the causes of easy falling of the roof of the cut hole, the L-shaped cut hole driving technology and surrounding rock supporting technology are proposed, and the deformation characteristics of surrounding rock of the cut hole under three different excavation methods, such as once-tunneling, secondary piloting tunnel and L-shaped cut hole, are compared and analyzed by numerical simulation. The results show that L-shaped hole cutting technology can effectively ensure the roof safety during hole cutting in three soft coal seams. The field test shows that the technology of grouting and anchor wire can control the deformation of surrounding rock with large span cut in three soft coal seams.