Lodging is one of the important factors affecting the high and stable yield of wheat worldwide. Solid-stemmed wheat has higher stem strength and lodging resistance than hollow-stemmed wheat. There are many solid stemmed varieties, landraces and old varieties of durum wheat. However, the transfer of solid stem genes from durum wheat is suppressed by the suppressor gene located on chromosome 3D in common wheat, and only hollow-stemmed lines have been created. However, synthetic hexaploid wheat can serve as a bridge to transfer solid stem genes from tetraploid wheat to common wheat. In this study, the F1, F2, and F2:3 generations of the cross between solid-stemmed Syn-SAU-119 and semisolid-stemmed Syn-SAU-117 were developed. A single dominant gene, tentatively designated Su-TdDof, was identified in synthetic hexaploid wheat Syn-SAU-117 by genetic analysis, which suppresses stem solidity. Using bulked segregant RNA-seq (BSR-seq) analysis, Su-TdDof was mapped to chromosome 7DS and flanked by markers KASP-669 and KASP-1055 within a 4.53 cM genetic interval corresponding to 3.86 Mb and 2.29Mb physical region in the Chinese Spring (IWGSC RefSeq v1.1) and Ae. tauschii (AL8/78 v4.0) genome, respectively, in which three genes related to solid stem development were annotated. Su-TdDof differed from a previously reported solid stem suppressor gene based on its origin and position. Su-TdDof would provide a valuable example for research on the suppression phenomenon. The flanking markers developed in this study would be useful for screening Ae. tauschii accessions with no suppressor gene (Su-TdDof) to develop more synthetic hexaploid wheat lines for wheat lodging resistance breeding and further cloning the suppressor gene Su-TdDof.