A method for separating the original image and the conjugate image in the reconstruction of Fourier computer generated hologram (CGH) was studied. According to the analysis on the process of CGH reconstruction by Fourier transform, the method which put the original sampling points into a larger null matrix was used to separate the original image and conjugate image. After the fast Fourier transform with the new matrix, CGH was obtained by Burch coding, then a high pass filter was used to eliminate the influences of interference of background light on the visual impression when image was
reconstructed. The degree of separation of the original image and the conjugate image of CGH produced by this method can be controlled with the size of the null matrix, the larger the null matrix, the greater the degree of separation. The experimental results show that the original image and conjugate image of CGH can separate when the null matrix is 4 times of the original size. But in order to filter the zero order light spot easily, the null matrix should be more than 4 times of the original size slightly.