The measuring principle of the grating autocollimator is discussed based on vertical stripes Moiré detection.Using the Fourier optics theory,it is able to deduce that the method is feasible which uses the linear array CCD to replace the instructions grating to produce moiré fringes in the autocollimator.The experiment validates that when the ratio s between projection grating constant d2 on CCD and grating constant d1 equals to 1.01,the amplification ratio of the vertical moiré fringes can reach to 14.14.The proposed method can solve the problem that the grating diffraction affects the trial result,simplify the autocollimator optical system,and enhance the system′s resolution.