The full spectrum k distribution (FSK) model, MIE theory and finite volume method (FVM) are applied to construct the radiation transfer model in the isothermal and homogeneous high temperature gas-soot mixtures. Under different soot sizes, different soot volume fractions, different path lengths and different temperatures, the calculated errors of radiative heat transfer properties (such as the radiative heat flux and radiative source term) due to neglecting the soot scattering effect are studied. The research results reveal that when increasing the soot size with the soot volume fraction unchanged, the calculated errors will increase first and then decrease. When increasing the soot size with the soot particle number density unchanged or increasing the volume fraction with the soot size unchanged, the calculated errors will increase monotonously. When the soot size and the volume fraction unchanged, increasing the radiative heat transfer path length or increasing the medium temperature, the calculated errors will also increase monotonously. Therefore, for high temperature gas-soot mixtures with large particles or large soot volume fraction, the soot scattering should not be ignored.