Computer simulation calculations have been carried out of precipitate recoil resolution under energetic particle irradiations. Using MARLOWE code, recoil range distributions in complete cascade events from primary recoils with energies between 1 to 100 keV are calculated in pure iron. From these results, precipitate shrinkage rate is estimated in various irradiation conditions. The resolution rate is found to be highly sensitive to projectile mass rather than projectile energy. This suggests a considerable difference of the resolution rate under heavy and light ion irradiations. Remarkable change in the precipitate size begins only after irradiations to several tens dpa. This implies that some precipitates, which are present at low to intermediate doses, can disappear at high doses by recoil resolution. It is shown, by comparison with fission neutron irradiation data, that the recoil resolution of tiny but numerous precipitates can be a factor to determine the incubation dose of void swelling.