When chemical oxygen-iodine laser (COIL) runs longtime, the influence on heating effects of mirrors has attracted attention abroad. For obtaining accurate estimate on it, relying on past experience, we carry on coupling simulation among flow field, optical field and heating effects of mirrors. At present computational condition, three-dimensional model about nozzle flow is constructed; by analyzing simulation data, coupling simulation result is obtained between flow field and optical field. Finally, the influence on heating effects of mirrors is investigated. The focus is solving the convergence of iteration between flow field and optical field. By particular analysis on the physical mechanism, coupling style is adjusted; finally, stable result is obtained, coupling iteration times is reduced greatly. The simulation result indicate if considering actual flow field disturbance, facular fragmentation is distinct; the disturbance exist from the beginning, so it influences on beam quality in the whole course.