The distribution of residual stresses was determined through the thickness of a 50-mm thick ferritic steel weld plate using (110) and/or (211) diffraction peaks. We proposed a two-peak combined methodology, which uses (110) and (211) peaks designed to have neutron wavelengths of 2.39 and 1.55 , respectively, in order to locate the neutron cross-section at each local minimum. The result shows that the available penetration path length can be maximized by (110) diffraction for the transmission geometry and (211) diffraction for the reflection geometry of the plate specimen. Furthermore, the stress components by the two peaks were similar to the results of the conventional one-peak measurement due to the same diffraction elastic constants between the (110) and (211) peaks in the bcc ferritic steel. Such appropriately combined two-peak method can significantly enhance the deep penetration capability for the determination of residual stresses in an extra thick steel plate specimen.