Virtual Reality (VR) products serve for human eyes ultimately, and the optical properties of VR optical systems must be consistent with the characteristic of human eyes. The monocular coaxial VR optical system is simulated in ZEMAX. A diffraction grating is added to the optical surface next to the eye, and the lights emitted from the diffraction grating are deflected, which can forming an asymmetrical field of view(FOV). Then the lateral chromatic aberration caused by the diffraction grating was corrected by the chromatic dispersion of the prism. Finally, the aspheric surface was added to further optimum design. During the optical design of the system, how to balance the dispersion of the diffraction grating and the prism is the main problem. The balance was achieved by adjusting the parameters of the grating and the prism constantly, and then using aspheric surfaces finally. In order to make the asymmetric FOV of the system consistent with the angle of the visual axis, and to ensure the stereo vision area clear, the smaller half FOV of monocular system is required to reach 30°. Eventually, a system with asymmetrical FOV of 30°+40° was designed. In addition, the aberration curve of the system was analyzed by ZEMAX, and the binocular FOV was calculated according to the principle of binocular overlap. The results show that the asymmetry of FOV of VR monocular optical system can fit to human eyes and the imaging quality match for the human visual characteristics. At the same time, the diffraction grating increases binocular FOV, which decreases the requirement for the design FOV of monocular system.