Irradiation-enhanced precipitation of Cu clusters is a main factor contributing to the hardening/embrittlement of reactor pressure vessels, and thus, limiting the lifetime of reactors. The Cu clusters are easily formed in ferric alloys under neutron irradiation or ion irradiation, which is used to simulate neutron irradiation. However, the inhibition and even dissolution of Cu clusters in Cu-containing alloys after ion irradiation is also observed in some research. To investigate the reason for ion irradiation-induced dissolution of solute clusters, Fe-1.3%Cu (atomic fraction) alloys were irradiated with Ar ions to the fluence of 4 × 10¹⁶ ion/cm² at 290^oC. TEM and atom probe tomography were used to characterize microstructure and solute atom distributions, respectively. Numerous black dot defects and bubbles with average diameters of about 1.3 nm are observed in the irradiated layer. Well-defined Cu-rich clusters are also precipitated in the irradiated layer. The average radius and number density of clusters increase first and then decrease with an increase in distance from the surface. The high displacement damage rate and large cascade size of Ar ions inhibit the irradiation-enhanced diffusion of Cu atoms and bring Cu atoms of the clusters back to matrix, which causes Cu clusters to precipitate weakly near the irradiated surface. With increasing distance from the surface, the Ar ion concentration increases. Ar-vacancy complexes or Ar bubbles form due to the aggregation of Ar ions. Then, the interattraction between Cu atoms and vacancies complexes would enhance the atom diffusion and segregation, which causes an increase in size and number density of the Cu-rich clusters.