The emission of an edge dislocation from a thin-film-covered crack is studied in order to investigate the effects of a passive film on stress-corrosion cracking. The results show that the crack stress field in the film due to the applied loads is enhanced by a harder film or abated by a softer film. For an edge dislocation is the film is harder. Under pure mode II or III loadings a harder thin film makes the dislocation emission easier and a softer film makes the dislocation emission more difficult if the film thickness is smaller than a critical value. The opposite is also true if the film thickness is larger than the critical value. Under pure mode I loadings, however, a harder thin film makes the dislocation emission more difficult and a softer film makes the dislocation emission easier for the two flim thicknesses used in this study.