Trehalose-6-phosphate synthase (TPS) is a key enzyme involved in the synthesis of trehalose and has been reported to participate in regulating photosynthesis, carbohydrate metabolism, growth and development, and stress responses in various species. Currently, reports on TPS genes in soybean are scarce. This study identified 20 soybean TPS genes and their associated 10 conserved protein motifs in the soybean genome. Molecular analysis of promoter elements showed that the TPS gene promoters are rich in stress-responsive elements. After salt stress treatment, the expression of 17 TPS genes changed, with 12 genes up-regulated and 5 genes down-regulated. Haplotype and selection analyses revealed two major allelic variations in TPS8, TPS13, TPS15, TPS17, and TPS18. Notably, variants carrying TPS15^H2、TPS13^H2、TPS17^H2 and TPS18^H2 were significantly enriched in improved cultivars that underwent strong artificial selection. This study reveals the molecular characteristics of the soybean TPS gene family, their expression patterns under salt stress, and their evolutionary history, providing theoretical basis and genetic material for further elucidating the functions of soybean TPS genes and breeding salt-tolerant soybean varieties.