Transformation of various intrinsic Frank loops into stacking-fault-tetrahedron（SFT）-like structures in single crystal copper is investigated using the molecular dynamics（MD） method. We got stable SFT structures and explained their formation via a unified theory.Simulation results show that there is a critical size for the Frank loops at zero temperature. When being smaller than this critical size, Frank loops can not transform into SFT. Hexagonal and trapezoidal Frank loops exhibit oscillations in the relaxation processe, which is due to the elastic interactions between dislocations as well as the delay effects in the propagation of elastic waves.