Abstract: During research this paper took cut open-off of 8206 fully mechanized face in southern 402 mining area of Jinhuagong Coal mine as object, analyzed failure feature of coal and rock and then put forward three main control index of surrounding rock stability consists of roof separation ration, loose coefficient of surrounding rock and development degree of fractures in surrounding rock. Then, we classified the control index of surrounding rock stability and based on this classification, the support difficulty is further dived into six grades by combining with roof property and actual support characteristics of surrounding rock. At last, by mans of calculation and classification table, support difficulty of 8206 cut open-off was determined as second grade, ie, hard to support. With the determination of its support difficulty, the cut open-off was applied to “trinity” comprehensive support system of which the control approach and acting mechanism were illustrated. Application of “trinity” system proved obvious control effort of the system. Meanwhile, the support concept and system provides some preference for cut open-off with similar conditions.

Key words: large-span cut open-off, roof separation rate, loose coefficient of surrounding rock, development degree of roof fracture, “trinity&rdquo, support system