Using X-ray reflectivity , we report the responses of the magnetic films under the application of magnetic field. A thin film sample of Pd/Fe/FeSi/Si was prepared for this study. Under the application of magnetic fields, we observed that the periodicity and the intensity of the fringes resulting from the constructive interference between the layers can be changed as the field strength exceeding a threshold value, suggesting the morphology, including the periodicity, thickness and roughness of the films have been changed by the applied fields. These changes are understood to be possibly caused by the re-arrangement of the Fe domains in the film by the fields