Based on the physical optics method, the scattering characteristics of fractal rough surface coated objects are studied in the terahertz (THz) range herein. A blunt model based on fractal rough surfaces is built. The surface current is calculated according to the Fresnel reflection coefficient, and the Radar Cross Section (RCS) of the rough coated target is obtained. The RCS of rough and smooth surface targets are compared. Numerical results for a rough coated blunt cone model are provided, and discussed from the perspective of different frequencies and coating thickness values. The results show that the surface roughness of the target has a significant effect on scattering in the terahertz range.