Abstract: The accurate mathematical externality of the target was established with surface generation method in computer graphics, which was dispersed into triangular facets. Relationships between the geometrical elements were described with topological structure. The method of shooting and bouncing rays was used to simulate the multiple-reflection of ray beam. The divergence factor, magnetic field direction and phase difference were educed. The far-field scattering was solved with physical optics integration at the final reflection point. Summing up the contribution from each ray beam, the value of coupled radar cross section was obtained. In order to reduce the calculation amount in the process of ray shooting and bouncing, an acceleration arithmetic was adopted. The calculation results of a wing-body combination were presented as a specific example.