The invention discloses a half-space Green function applied to an electromagnetic scattering simulation model and a ray tracing method. The method comprises the steps that a target model with electrical characteristics being metal characteristics and a rough surface below the target model are determined, wherein the rough surface is located on an XOY coordinate plane, the height mean value of the rough surface is z which is equal to 0, the target model is located above the rough surface, and geometrical information of the target model is obtained according to subdivision of the target model; the rough surface under radar illumination is removed, a bounding box is adopted to surround the target model, and the bounding box is stretched in the -z direction to -z; and the ray tracing method is adopted to perform tracing judgment and other operation on the target model to obtain an electromagnetic induction current, the half-space Green function and a radar scattering field under a far-field condition. According to the scheme, the principle is adopted to solve difference field radar cross section echo information of a target located on the random rough surface, and the calculation precision and efficiency of an electromagnetic simulation algorithm are improved.