Transient coupled radiative and conductive heat transfer in a three-layer absorbing and isotropically scattering composite with semitransparent specular interfaces and surfaces is investigated. The transient energy equation is solved by the full implicit control-volume method in combination with spectral band model. The radiative heat source term is calculated by the radiative transfer coefficients (RTCs), which are deduced by the ray tracing method in combination with Hottel and Sarofim’s zonal method (Hottel H. C., and Sarofim A. F., 1967, Radiative Transfer, McGraw-Hill Book Company, New York). The effects of extinction coefficient, refractive index, and scattering albedo etc., on coupled heat transfer are studied under radiative and convective boundary conditions. The effect of isolating space on coupled heat transfer and the appearance of temperature peaks within the composite are investigated. It is found that temperature peaks also appear in the inner parts of an inhomogeneous semitransparent medium layer even though there is no convection cooling on the surfaces. This occurs when the absorbing coefficient of inner parts is higher than that of the parts close to the surfaces, and the two surfaces are semitransparent and subjected to an external radiation.