Abstract: Based on the fracture behavior of single closed crack in infinite plate of fracture mechanics, the effect of crack orientation β, length a and friction coefficient f_w on crack strength were discussed and compared with the fracture behavior of rock block by the Coulomb -Mohr's criterion according to type II crack's fracture criterion and analytical expression of the bursting strength of crack under uniaxial compression. The effect of crack on fracture behavior of coal and rock mass are discussed. The results show that the strength and the way of fracture of coal and rock mass with a single closed crack under uniaxial compression are controlled by the crack's strength and the strength of rock block; the more closer the crack orientation is to its dominance orientation β_m of broken, the more larger the length is, the more smaller friction coefficient is, the smaller the strength of crack is and the more likely that coal and rock mass burst along the crack surface. Its strength is controlled by crack surface strength.