In this paper, the ES-DRESOR method, an equation-solving method to calculate the DRESOR values differently from the MCM used before, is proposed. In this method, a unit blackbody emission is supposed within a cell, while there is no emission from the remaining part of the system. This leads to the equations for the DRESOR values based on the incident radiation, and all the DRESOR values can be solved directly from the equations without the rays tracing used in the MCM. Numerical results show an excellent agreement of all DRESOR values found by ES-DRESOR method and MCM for 100 cells in 1D case with emitting, absorbing, and isotropic scattering medium and transparent boundaries. The average relative error for the intensity obtained by the ES-DRESOR method is only 3.372 x 10(-5), lower by one order of magnitude than 4.022 x 10(-4) obtained by the MCM under the same conditions. The CPU time for computing the DRESOR values using the MCM varies from a few hundred seconds to several thousand seconds. In contrast, it is less than 1 s using the ES-DRESOR method, showing an obvious improvement in the computational efficiency. (C) 2012 Elsevier Ltd. All rights reserved.