Abstract: On the basis of the two-flux model of radiative transfer in photochemical reactor, the model was extended by considering light transmission passing through the photocatalyst, and reflection and absorption of light by the photocatalyst in the plane parallel-plate reactor. The extended model showed the dimensionless radiation intensity distribution and the dimensionless total radiative energy absorption rate in heterogeneous photoreactor. Semiconductor ultrafine TiO 2 power was widely used as the photocatalyst in heterogeneous photochemical reactor for environmental control. In order to show the usefulness of this simple method, the effects of TiO 2 power diameter and reactor depth on the dimensionless radiation intensity distribution and on the dimensionless total radiative energy absorption rate in gas-solid heterogeneous photocatalytic reactor were illustrated. The model explained that it was necessary to select reasonable reactor depth, particle diameter and density on semiconductor heterogeneous photoreactor designed.