<p>This paper presents a theoretical model of dislocation penetration through grain boundaries (GBs) in micro-crystalline materials, taking into account the interactions between dislocations and GBs in a hydrogen environment. It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials, and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains. The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains. Moreover, the presence of hydrogen further decreases this distribution area, suggesting a reduction in dislocations emitted in a hydrogen environment. Consequently, this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack, promoting increased crack propagation. The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%. These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.</p>