The experimental and theoretical studies of evolution of nanocavities in argon-irradiated copper under annealing are presented. The subsurface argon-filled nanocavities are formed during a short annealing at a temperature around 1000 K by migration and interaction of complexes of the simplest defects created by argon irradiation at room temperature. A long-time annealing at a temperature above 1075 K leads to decomposition of nanocavities and desorption of argon from the sample. Using the X-ray photoelectron spectroscopy and scanning tunneling microscopy and spectroscopy, valuable data sets including the density of nanocavities and their size and depth distribution are obtained. A theoretical model describing the nucleation and evolution of nanocavities is developed. Computer simulations based on this model show that the nanocavities grow at elevated temperatures by absorption of argon–vacancy complexes formed during the ion irradiation. By comparison the calculations with experimental results, the migration energy of these complexes is estimated to be around 2.5–2.75 eV. Also, the value of dissociation energy of a complex, consisting of two vacancies and two argon atoms, is found to be equal to approximately 1.10–1.18 eV. The calculation of concentration of nanocavities at different annealing conditions reveals a satisfactory agreement with the experimental observations.