This study adopts the cohesive element technology for the first time to analyze the dynamic evolution process of crack formation and propagation, and to clarify the mechanical mechanism of the "O-X" failure pattern in the roof. The mechanical behavior of cohesive failure inside the rock is simulated based on the maximum nominal stress criterion, and the Benzeggagh-Kenane (BK) fracture criterion is used to further describe the dependence of fracture energy on the combination of mixed tensile-shear mode. The results show that the "O"-shaped crack is formed on the top surface of the roof, and delamination occurs along the thickness direction, which coincides with the crack bifurcation position on the bottom surface of the roof. The "cross"-shaped crack forms on the center of the bottom surface of the roof, and extends towards the four corners at the bifurcation position to form a spatial "X"-shaped crack.