A simple and practical method, moiré fringe method (MFM), for adjusting the light path of the pulse compression grating with a great aperture is introduced, with which the longitudinal precision of the conventional light path adjustment is improved. With the imaging formula of the holographic lens, the principle of the light path adjustment is deduced. With the primary aberration theory and relationship between the optical recording system and the diffraction wavefront aberration of the grating, it is concluded that the aberration of the moiré fringe is 0.4786λ, approximately twice of the diffraction wavefront aberration of grating. According to the above numerical relation, the diffraction wavefront aberration of the grating can be monitored. From the simulation, it is presented that, the wavefront aberration can be reduced to 0.06λ, corresponding to the longitudinal error of 0.007 mm.