The thermal stability of Cu specimens subjected to high–pressure torsion (HPT) deformation with varying strains was studied by optical icroscope (OM), differential scanning calorimetry (DSC) and transmission electron microscope (TEM). It is found that cellular subgrains with high dislocation densities are firstly formed at a low strain level, some of the cellular subgrains are transformed into dislocation–free equiaxed grains at larger strains. A single exothermal peak between 150 and 250 ℃ is shown in DSC curves, corresponding to the heat release due to recrystallization and subsequent grain growth. With the increase of strain, the peak position is shifted to a lower temperature and then is leveled off, but the stored energy of cold work, calculated according to the area under a peak, increases with strain at relatively low strain level and reaches its maximum value of 0.91 J/mol at strain of 13. Further deformation induces the stored energy of cold work to decrease due to the dynamic recovery of microstructure. A large drop in hardness appears in as–deformed samples at a temperature 45 ℃ lower than the start temperature of the exothermal peak after isochronal annealing, indicating that the recrystallization and grain growth process is closely relatine to annealing time and temperatur.