Null interference technology based on the computer generated hologram (CGH) has been used to measure the aspheric surface. For measuring deep aspheric surface with great deviation degree and high slope, it is difficult to fabricate CGHs with high spatial frequency. We proposes a method combining CGHs with low spatial frequency to achieve the function of a single high-spatial frequency CGH in deep aspheric surface test. A one-dimensional linear grating model is introduced to establish the relationship between the spatial frequency of the single CGH and that of CGHs combination, and the initial phase of the CGHs combination can be obtained based on the relationship. The optimal phase is solved out by optimization. For the deep aspheric surface with maximum departure of 193.434 μm and slope of 75.788 μm/mm, the wavefront errors for the single CGH and the CGHs combination are less than λ/250. The maximum spatial frequency of CGHs combination is reduced by 50% compared to that of the single CGH. Auxiliary alignment CGH is designed to reduce the adjustment errors, and the influence of tilt error, decentration and axial deviation on the detection accuracy is analyzed.