In this study, influences of participating media and wall surfaces on heat transfer of turbulent natural convection of a differentially heated cubic cavity were investigated. Coupled calculation of the convective and radiative heat transfers was conducted using the large eddy simulation (LES). To calculate the radiative heat transfer, the Radiation element method by the ray emission model (REM2) was utilized. The non-gray participating media was modelled by the full spectrum k-distribution (FSK) model, which accounts for the wavelength dependency of the absorption coefficient. Changing emissivity, specular, and diffuse reflectance of surrounding walls, the effect of the wall surface was studied. The calculation conditions with black body, specular and diffuse surface were investigated. When the surrounding walls were black bodies, flow instability increased strongly. Contrary to the black body conditions, the flow instabilities under the specular and diffuse surface conditions were weak and the radiative heat transfers from heated wall were almost same with the specular and diffuse surfaces. To investigate the influence of the participating media on the heat transfer, the concentration of the participating media was changed. When the concentration of the participating media was higher, the flow instability was enhanced while convective heat transfer was not affected.