Abstract: Natural rock masses often contain discontinuities，such as pores，fissures，fractures and other defects. The existence of these defects can greatly degrade the mechanical strength of rock. In order to study the effects of different crack geometries on the mechanical properties，crack propagation and fracture evolution mechanisms of fractured sandstone，based on the test results of mechanical parameters of sandstone in laboratory，a series of simulation studies on the fissured samples were carried out by means of the particle flow parallel bonding model firstly. The results show that when the flaw inclination angle is constant，the peak stress and peak strain of sandstone decrease first and then increase with the increase of ligament angle. When the ligament angle is constant，the peak stress and peak strain increase with the increase of flaw inclination angle. The initial crack originates from the pre-existing crack tip and the cracking stress level is 0.68σc. The cumulative microcracks of sandstone increase exponentially with the increase of axial strain. The failure mode of the specimen mainly includes tensile failure，shear failure and tensile-shear mixture failure. The coalescence mode of the ligament mainly includes direct coalescence and indirect coalescence.

Key words: Pre-existing flaw, Crack propagation, PFC2D, Parallel bonded model, Strain energy