The influence of the deviation angle of the sample surface from the exact crystalline surface on the X-ray double crystal rocking curves an{d its full width at half maximum (FWHM) were investigated based on the X-ray dynamical diffraction theory. The results show that when the sample surface has a deviation from the exact crystalline surface, the profile of rocking curves and their FWHMs are dependent on the incident angle and the direction of X-ray beam. Moreover, with the decreasing of the incident angle, the FWHM of rocking curve increases, and the reflection peaks shift to the high angle region. This influence becomes more significant when the asymmetrical diffraction is used.