Abstract: Ray-tracing is a key step to apply uniform geometrical theory of diffraction (UTD) in solving the problems of radiating and scattering by electrically large objects. An equation of one variable and four order for reflection points on spheres was deduced according to the reflection principle. Some reflection points were got based on the equation, and the far field pattern of a half-wave dipole near a sphere-cylinder model was given. The UTD result is proved correct by comparing it with the FEKO result. Simultaneously the tracing time is dramatically reduced and the operational precision is improved.