Molecular dynamics simulations were performed to study the plastic deformation of Cu films under uniaxial tension. The generation and evolution mechanisms of vacancy-type defects were carefully studied. In the simulations, embedded atom method (EAM) was selected as the interatomic potential function. Simulation results indicate that the plastic deformation is due to the dislocation nucleation near free surfaces. Both the generation and evolution of vacancy-type defects are related to dislocation activities. Vacancy-type defects prefer to nucleate at the position of dislocation jogs and the intersection of stacking faults initially, and finally exist in the form of single vacancy, vacancy clusters and stacking-fault tetrahedrons.