Expression of the reflex effect of natural lighting is a key problem of optic character simulation. The difference among the optic reflex character models of several target surface material facets, such as the facet's BRDF, experimental fit curve and expression of Phong in OpenGL, is analyzed. The material optic distribution in sun and sky (or earth) lighting is derived using the facet's BRDF. The effect of simplified OpenGL model on simulation of optic character is discussed. Based on OpenGL system, the methods of setting up 3D model and choosing material's optic parameter are given. The algorithm of complex target's optic character simulation in natural lighting is proposed and the result of the simulation is also presented.