Objective A mouse model of ulcerative colitis with spleen deficiency and dampness syndrome was established, and the function of T lymphocytes in this model was studied. Methods C57BL/6 mice were randomly divided into Control, FXY (folium sennae), 3%DSS (dextran sulfate sodium salt, DSS), FXY + 3%DSS, and FXY + 2%DSS groups. A mouse model of ulcerative colitis with spleen deficiency and dampness syndrome was established by DSS and senna leaf. At the end of modeling, HE (hematoxylin-eosin) staining was performed to observe structural changes in colon tissues. ELISA (enzyme-linked immunosorbent assay) was performed to measure the concentrations of proinflammatory cytokines in colon tissues. Flow cytometry was used to analyze CD4/ CD8 T lymphocytes, Th1/ Th2 cells, and Th17/ Treg cells. Results In the FXY group, the clinical symptoms of mice with spleen deficiency and dampness were mainly diarrhea, and mice treated with 3%DSS colitis mostly showed blood in stool, whereas mice with spleen deficiency and dampness colitis in FXY + 3%DSS and FXY + 2%DSS groups mostly showed diarrhea and blood in stool, but the survival rate of mice in the FXY + 3%DSS group was as low as 50%. Compared with the Control group, body weight, colon length, and concentrations of anti-inflammatory cytokines IL-10 and TGF-β1 were significantly lower in 3%DSS group, FXY + 3% DSS group, and FXY + 2%DSS group, while the DAI (disease activity index) concentration, colon weight, colon weight index, colon weight/ colon length, and proinflammatory cytokines TNF-α, IL-1β, and IL-6 were significantly increased, and significant ulcer formation and inflammatory cell infiltration were observed by light microscopy. Compared with the Control group, the percentages of CD4, Th1, and Th17 cells in mesenteric lymph nodes of FXY + 3%DSS group and FXY + 2%DSS group were significantly increased, while CD8, Th2, and Treg cells were significantly decreased. Conclusions The combination of senna and 2%DSS successfully establishes a model with ulcerative colitis with spleen deficiency and dampness evidence in mice, showing typical CD4/ CD8, Th1/ Th2, and Th17/ Treg cell imbalances.