In this study, a novel total spectrum-based non-gray model is proposed by modifying the narrow band based WSGG regrouping (RG-NBW) method. Using the total weighting factor and the total absorption coefficient for each gray gas group, the required number to solve the RTE can be remarkably reduced. To verify the performance of the modified RG-NBW, three-dimensional radiative transfer problems using pure H2O gas with a uniform temperature, a non-homogeneous mixture of H2O and N-2 with a uniform temperature, and a mixture of CO2, H2O and N-2 with a non-uniform temperature were solved using the discrete ordinate method (DOM) with various non-gray models. The results are compared to benchmark data obtained using the ray-tracing method with the statistical narrow band (SNB) model. For all cases, the results with the modified RG-NBW model show good agreement with the benchmark results as well as results from other models. Furthermore, the modified RG-NBW model requires the shortest computational time after the WSGG model. Therefore, considering the accuracy and computational time, the modified RG-NBW model can be an efficient choice for non-gray gas radiation problems. (C) 2017 Elsevier Ltd. All rights reserved.