This paper reports the investigation of the X-ray Bragg diffraction on a multilayer mirror modulated by a short wavelength (12 μm) surface acoustic wave. Useful parameters to determine the diffraction pattern are the amplitude, the period of the surface acoustic wave, and the deviation of the incident angle from the exact Bragg position. It is shown that changing the incident angle induces some variations in the distribution of the diffracted intensity between the diffraction orders. A model based on the dynamic diffraction theory has been developed and is compared to the experimental results.