Understanding the effects of heavy ion irradiation on the tensile properties of metals at the nanoscale is important for the development of nanomechanical and other nanodevices using focused ion beam fabrication. This is both in terms of achieving the expected performance of designed devices and in potentially exploiting changes in mechanical properties to develop novel device concepts. We report investigation of the tensile properties of gold nanocrystalline films bombarded by high-energy Ga ions using molecular dynamics calculations. Ga ion irradiation leads to multiple grains with the redistribution of the grain boundaries (GBs). Importantly, Ga ion irradiation causes the film to become less ductile and more prone to fracture. The main reason is not surface damage caused by the sputtering effect of high-energy particles, but the convergence of GBs to the surface crater. On the other hand, for porous films with micropores in the GBs, irradiation results in the hardening of film and the ultimate tensile strength is larger than that of unirradiated counterpart.