The dioptic system of compound eye of Beijing firefly was simulated on the basis of the real parameters measured from it's structure physiology and it's known GRIN lens properties.The size of the model and values of refractive index were based upon the measured values of actual compoune eye.It was proved that the compound eye of Beijing firefly was a refracting superposition eye by the computer ray tracing model of the compound eye.Parallel light rays incident through the superposition aperture were focussed across the clear zone onto the retina and formed a blur-circle with a certain half-width value. The number of signal light rays and the ratio of signal and noise were increased as the distance to the image plane from exocone proxmal tip were increased. The maxtmun was at the retina level.