Soil salinization severely constrains agricultural productivity, particularly affecting forage crops in arid regions. Although smooth bromegrass (Bromus inermis L.) demonstrates a certain level of tolerance, the candidate genes responsible for its resistance to saline-alkali stress remain largely unidentified. This study initially developed a high-quality, full-length reference transcriptome by sequencing a combined RNA sample, resulting in 124,616 unique transcripts with high completeness. Of these, 12,290 genes were annotated using various databases. Using this reference, transcriptome analysis was conducted on samples collected at different time points under salt and alkali stress. Analysis of differentially expressed genes, combined with physiological data and functional enrichment, indicates that 12 h is a key threshold in the response to saline-alkali stress. We identified 71 and 73 differentially co-expressed genes under salt and alkali stress conditions, respectively, with 15 upregulated genes shared by both stress types. KEGG enrichment analysis identified dynamic expression patterns in pathways crucial for stress adaptation, including phenylpropanoid and flavonoid biosynthesis, photosynthetic antenna proteins, plant hormone signaling, and nitrogen metabolism. Among these pathways, we identified six photosynthetic antenna protein genes, two SnRK2 genes, and one IAA gene that were consistently differentially expressed across different growth stages. Validation through yeast heterologous expression demonstrated that four genes Bromus_inermis_049541, Bromus_inermis_074327, Bromus_inermis_262350, and Bromus_inermis_001261 enhances tolerance to salt and alkali stresses; Bromus_inermis_142424 enhances alkali tolerance, whilst Bromu-s_inermis_295092 enhances salt tolerance. These findings provide candidate genes crucial for elucidating the molecular mechanisms underlying smooth bromegrass's tolerance to salt and alkali stresses, and offer direction for subsequent functional validation studies.