<p>Gradient-structured (GS) metallic polycrystals exhibit significant potential for integrating strength, ductility, and toughness. Enhancing our understanding of the relationship between their microstructure and mechanical properties of GS polycrystals is essential for optimizing the properties of materials. In this paper, a discrete dislocation dynamics model within the framework of state-based peridynamics (DDD-SBPD) is developed to investigate the elastoplastic deformation and fracture in GS polycrystals. By solving typical boundary value problems and comparing the DDD-SBPD simulation results with those from traditional DDD simulations and theoretical solutions, the DDD-SBPD model is validated. The model is then applied to simulate elastoplastic fracture in GS and homogeneous-structured (HS) polycrystals. By incorporating the intrinsic interaction between grain boundaries and dislocations, the model successfully captures the crack oscillations observed in the experiments. The relationships between the mechanical properties (e.g., strength, ductility, and fracture resistance) of metallic polycrystals and their structure are systematically analyzed. The results demonstrate that GS polycrystals outperform HS polycrystals in achieving a superior balance of mechanical properties, and that gradient orientation has a significant effect on these properties.</p>