The invention relates to a near-field holographic dynamic exposure method for suppressing secondary interference of a phase mask in a direction perpendicular to a grating vector, which belongs to the technical field of diffraction grating preparation. In near-field holographic exposure, the initial secondary interference pattern of a phase mask in a direction perpendicular to a grating vector is suppressed through micro displacement in the direction perpendicular to the grating vector. Thus, the stray light level of prepared gratings is reduced, and the duty cycle uniformity of gratings is improved.