Transient heat transfer of coupled radiation and conduction inside a semitransparent composite slab of absorbing-emitting-anisotropic scattering medium is examined. The composite slab includes two layers with different physical properties. Surfaces and interface between two layers are supposed to be semitransparent and total reflection will occur there at the critical angle. Specular reflection is considered and reflectivities are determined by Fresnel's law and Snell's law. A fully implicit control-volume method is used to solve the transient energy equation and a ray-tracing/nodal-analyzing method is used to compute the radiative information. A criterion for total reflection is proposed for solving the problem of integral singularity at the critical angle. Effects of conduction-radiation parameter, scattering albedo and refractive index on coupled heat transfer are investigated. Results show that in a semitransparent medium with natural surfaces, there are two sorts of temperature peaks appearing at transient heat transfer: one is caused by external radiation heating and environmental convection cooling, still existing in steady state; the other is due to maximum of absorption of heat caused by inhomogeneous optical properties, only existing in transients of heat transfer. (c) 2008 Elsevier Ltd. All rights reserved.