In this study, extensive molecular dynamics simulations were carried out to investigate failure processes along different symmetric tilt grain boundaries (STGB) of bicrystal graphene sheet. Two different types of STGBs graphene mainly zigzag and arm-chair types were investigated. The dependence of fracture strength, strain as well as Young's moduli on different STGBs were examined. The results clearly show that pristine graphene has the highest values of fracture strength and strain to fracture. Furthermore, bicrystal graphene with zigzag-oriented grain boundaries have improved mechanical properties in comparison to those with arm-chair oriented grain boundaries. Fracture behavior was investigated by applying mode I loadings to the outer boundary of bicrystalline graphene sheet with several misorientation angles. The critical stress intensity factors (SIFs) are calculated as a function of displacement were determined by using crack-tip opening displacements (CTOD) at the incipient bond breaking. The atomistic results show that the crack propagation along armchair-orientation grain boundaries are faster than that of zigzag-orientation grain boundaries of bicrystal graphene.