Coherent scattering and incoherent scattering can be both found in the scattering research of terahertz wave on rough metal sphere target. Coherent scattering mainly happens in low frequency region, which will decrease rapidly as the sphere roughness increase. Incoherent scattering is mostly found in high frequency region, which is related to the mode and the regularity of radiation distribution as well. According to the study, the scattering results in low and high frequency regions are quite different from each other. The two scattering results appear to be approximately consistent when the sphere roughness is in Gaussian distribution.