Triple negative breast cancer (TNBC) is a highly aggressive subtype with a poor prognosis due to its high rates of proliferation and metastasis. Recently, hydrogen sulfide (H₂S) has been recognized as a novel gasotransmitter that plays a significant role in various pathological processes, including cancer. Here, we show that exogenous H₂S inhibited TNBC cancer cell proliferation, migration and invasion in vitro, and also decreased cancer malignances in the mouse model of TNBC. To investigate the underlying mechanisms of H₂S's anti-cancer effects in TNBC, we performed transcriptome sequencing and bioinformatic analyses. 2121 differentially expressed genes (DEGs) were revealed, and mainly enriched in cell cycle and DNA replication pathways. Further analysis revealed changes in alternative splicing after exogenous H₂S treatment. Protein-protein interaction (PPI) network analysis was performed, which identified 458 interactions among 276 DEGs enriched in cell cycle and DNA replication pathways.We identified seven hub genes (MCM3, MCM4, MCM5, MCM6, CDC6, CDC45, and GINS2) through PPI network analysis, which were up-regulated in clinical human breast cancer but down-regulated after H₂S treatment. Based on the hub genes selected, we developed a model predicting that exogenous H₂S mainly exerts its anti-TNBC role by delaying DNA replication. Our findings suggest that exogenous H₂S has potential as a therapeutic agent in TNBC and may exert its therapeutic potential through DNA replication and the cell cycle pathway.