Abstract: The crack propagation and strength of fissured rocks under applying loads are significant for the study of rock deformation mechanism. Mortar fractured specimens have been simulated as fissured rock in the uniaxial compression experiment. Different crack length, the initial propagation angle of specimens and initial crack strength have been obtained by setting 9 experimental conditions. They have 3angles of 45, 60 and 75 and 3 crack length of 45mm, 60mm and 75mm. The compression failure mechanism is also analyzed. The results show the following. When the crack length is the same, the initial crack strength is increased by the increase of angles. When the angle is increased from 60to 75,the initial crack strength is increased faster. When the crack angle stays at a certain level, the initial crack strength is decreased by the increase of the crack length. By employing the theory of maximum circumferential stress, the failure mechanism of fractured specimens under compression is interpreted. Theoretical expression of crack propagation angle is acquired. By comparison, it is found that the measured and theoretical values of crack propagation angle are in good agreement.