A new test method based on a Computer-generate Hologram(CGH) was presented for precisely testing off-axis aspheric surfaces and aligning the optics in tests. In this method, off-axis aspheric surfaces were tilt-translated and tested as an on-axis freeform optics to minimize the wavefront compensation and to reduce the relative aperture of the test setup. A software was developed to design the CGH to implement three kinds of diffractive sections,i.e. compensating wavefront in null test, alignmenting the optical path by adjusting the relative position between CGH and interferometer, and projecting fiducial marks around the optics. As an example, a typical off-axis aspheric surface with a figure error less than λ/50 rms was tested in this method. Results indicate that the CGH design error is better than λ/10 000 rms and the total error is better than λ/100 rms.These data agree well with the test result with null lens. The experiment also verifies the feasibility of alignment and fiducial sections and demonstrates that cross-lines projected by CGHs can be used as fiduciary to guide the alignment of the optics and measure the off-axis distance.