Molecular dynamics simulations are employed to analyze the tension mechanical properties of single-crystalline nano-Cu films. Attention is directed to elucidate the microstructure evolution and deformation mechanisms. Computational results show that the plastic deformation mechanism of the {100} oriented nano-Cu films is more likely due to short-distance sliding of the atoms, which results in the formation of stacking faults, microtwins, dislocation locks and vacancies. In particular, vacancy generation and migration in the film are carefully examined at the atomistic scale, which is closely related with the intersection of stacking faults and the gliding of jogged dislocations.