High molecular weight glutenin subunits (HMW-GS) and Low molecular weight glutenin subunits (LMW-GS) in mature grains play important roles in the formation of glutenin macropolymer and gluten quality. To characterize the expressed glutenin genes of the bread wheat variety Xinmai 26 during seed development, in this study, we measured the dough rheological properties of mature grains through farinograph and gluten testing system, and revealed its strong gluten quality. The compositions of HMW-GS and LMW-GS were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Further, a total of 18 full-length transcripts were obtained by third-generation RNA sequencing, including 5 transcripts of HMW-GS genes and 13 transcripts of LMW-GS genes (8 intact genes and 5 pseudogenes). The deduced protein structures of transcript sequences exhibit the typical HMW-GS and LMW-GS structural characteristics. Moreover, a specific functional marker was developed to make better use of the extra cysteine residue of 1Dx5 subunit. This study provides an efficient method to accurately identify glutenin genes in bread wheat through matching full-length transcripts to their spectrum of glutenin, which will be helpful to understand the contributions of glutenin genes to wheat quality.