<p>As one of the primary materials used in fusion reactors, tungsten is exposed to radiation and stress during operation. However, the effect of the interaction between radiation-induced defects and grain boundaries (GBs) in tungsten on its mechanical response remains unclear. Molecular dynamics (MD) simulations are applied to investigate the evolution of radiation-induced defects in single-crystal and bicrystal tungsten at different temperatures and energies of primary knocked-on atom (PKA). The mechanical response of tungsten at different cascading collisions stages was also studied. The results indicate that while there is no significant correlation between temperature and defects, the number of defects in both single-crystal and bicrystal tungsten is positively correlated with the PKA energy. The segregation of interstitial atoms at GB reduced the number of defects within the crystal at the thermal spike stage. But it also inhibited the interstitial atoms bind with vacancies, resulting in an increase in the number of defects at the stable stage. Additionally, irradiation caused a large drop in the yield stress of single-crystal tungsten, whereas irradiation caused little change in the yield stress of bicrystal tungsten. The maximum dislocation density of irradiated bicrystals is significantly lower than that of non-irradiated bicrystals. In irradiated single-crystal tungsten, dislocations nucleated prematurely at radiation-induced defects, whereas GB is the site of dislocation nucleation both before and after irradiation, so the yield stress of bicrystal tungsten did not decrease. However, GB is susceptible to fracture after irradiation, which is related to the promotion of crack formation by interstitial atoms segregated at GB.</p>