In this research simulation of crack propagation in three-dimensional Fe-bicrystal has been done by molecular dynamics in order to consider fracture resistance of ?5(310) and ?5(210) symmetric tilt grain boundary. The fracture resistance of ?5(310) symmetric tilt grain boundary has been compared with ?5(210) symmetric tilt grain boundary in terms of crack length-time curve, temperature per time diagram, and the stress-strain curve. Crack delay time at the grain boundary is a parameter used in this study to consider fracture resistance of grain boundary, which can be obtained from crack length per time diagram. The results show crack delay time at the grain boundary is inversely related to the grain boundary energy. Thus, crack delay time at the of ?5(310) symmetric tilt grain boundary with 986 mj/m 2 energy is more than ?5(210) symmetric tilt grain boundary with 1098 mj/m 2 energy. The Increasing amount of stress, which is needed to overcome the grain boundary resistance and cause to crack penetration into the subsequent grain, has been calculated by the stress-strain curve. In the following, the atomic configuration of Fe-bicrystal with ?5(310) symmetric tilt grain boundary is considered along with the crack propagation procedure, and the defect analysis in the bicrystal has been done by BDA algorithm and centrosymmetry parameter. In the end, in order to study the effects of temperature, crack propagation was considered in Fe-bicrystal with ?5(310) symmetric tilt grain boundary at 300 Kelvin. Keywords : Molecular dynamic simulation, Crack propagation, Fe-bicrystal, LAMMPS