Abstract: Three-dimensional flow governing functions and the paraxial wave function are solved within whole laser cavity for the study of supersonic chemical oxygen-iodine lasers. A suitable computational method is developed to improve compatibility, effectiveness of data communication, and convergence performance for the coupling of computational fluid dynamics and computational optics. The coupled simulation can provide detailed information about the three-dimensional mixing flow in the cavity, the diffraction of resonant optical field, the influence of laser extraction upon flow fields, and the intensity and phase distribution of laser output.