Abstract: In the DMD (Digital Micromirror Devices) based computational holographic system, the zero-level spot and the multi-level diffraction have great impacts on the quality of the optically reconstructed image. An improved optical path system is proposed to optimize the quality of computer-generated hologram (CGH) reconstruction images in this paper. With G-S algorithm, a lens and a diaphragm are added behind the spatial light modulator (SLM). The light reflected by the SLM is converged after passing through the Fourier lens. Diaphragm is placed on the back focal plane of the Fourier lens. By shifting the position of the diaphragm left and right, the diaphragm is placed in the center of the zero-order spot and multi-order diffraction. Consequently, high-quality reconstructed images are obtained due to the filtering out of the zero-order speckle and multi-order diffraction. The optical path in this work can also save space occupancy. Experiments are validated using 2D letter “CGH” and 3D teapot images to demonstrate the feasibility of the method in general.