The invention discloses a pre-evaluation system for accelerating computation of target radar scattering cross section by graphical electromagnetic computation through index information. The system comprises a surface element modeling module (1), an index information compilation module (2), an entity display module (3), an index information unscrambling module (4), a geometric information analysismodule (5) and a target radar scattering cross section acquisition module (6). The surface elements of a target model are numbered, an index list of the surface elements is established, the surface element index and the surface element color are subject to one to one correspondence, the background color is set as black, components of three primary colors namely red, green and blue are zero, the surface element blanking is finished by a GPU, the corresponding surface element index is obtained by the color of pixels so as to obtain normal vectors and depth values of the pixels. The whole process needs no illumination, the surface normal vector is pre-obtained in a drawing process of the surface elements, a color value is read only for once, and twice memory exchange is executed, which is one computation less than the normal graphical electromagnetic computation, thus shortening the computation time.