Abstract: To solve the problem that extra-thick compound roof in Guiqing Coal Mine is easy to cause abscission layer failure and improper maintenance of roadway is easy to lead to large area roof caving accident, based on the theoretical analysis and numerical modeling, we discuss the reasons that extra-thick compound roof rock beam occurs abscission layers and failure features, and reveal the damage laws of rock beam. The results show that the abscission layer failure of compound roof occurs on the both sides of rock beam and then extends to the middle of rock beam; the initial position of rupture failure on both sides of rock beam occurs on the upper end and the lower end in the middle of rock beam. The causal relationship of roadway instability with extra-thick compound roof is joint fissure or fault structure development, low roof rock mass strength, lower rock beam deformation, fracture, abscission layer failure, upper rock beam abscission, fracture failure, surrounding rock instability.