Objective To explore the clinical curative effect of modified Sijunzi decoction on adjuvant che⁃ motherapy for colorectal cancer and its effect on the tumor microenvironment of patients receiving chemotherapy. Methods The clinical data of 30 patients with colorectal cancer who received chemotherapy were retrospectively analyzed. They were divided into combined treatment group and control group according to whether they took Sijunzi decoction during chemotherapy. Single ⁃cell RNA ⁃sequencing of paired tumor tissues from the same patient before and after treatment was performed. Results Fifteen patients were included in the combined treatment group and the control group，respectively. There was no statistically significant difference between the two groups in terms of gender composition，age，colorectal cancer stage，and differentiation. After treatment，the TCM symptom scores of anorexia（P < 0.05），loss of spirit（P < 0.05），abdominal distension（P < 0.05）and loose stools（P < 0.05）in the combined treatment group were lower than those of the control group，and the differences were statistically significant. Analysis of single ⁃cell sequencing data revealed that the proportion of CD8 + T cells was higher in the combined treatment group after treatment compared with the control group，and the TNF ⁃α/NF ⁃kB signaling path⁃ way，IL6/JAK/STAT3 signaling pathway，and IL2/STAT5 signaling were activated in CD8 + T cells in the combined treatment group. In addition，comparison of differential genes of effector T cells in the two groups showed that effector T cells in the combined treatment group highly expressed genes such as LTB and IL7R after treatment. The effector T cell function was activated in the combination treatment group，which may be related to the increased activity of TNF⁃ α/NF⁃kB pathway and IL2/STAT5 pathway. Finally，modified Sijunzi decoction may also play a potential therapeutic role by activating macrophage phagocytosis and promoting cellular interactions between macrophages and effector T cells. Conclusion Modified Sijunzi decoction was effective for patients with colorectal cancer undergoing chemo⁃ therapy，and could significantly improve the quality of life of patients. Modified Sijunzi decoction has a significant effect on the tumor microenvironment of colorectal cancer patients undergoing chemotherapy，which may play a role by enhancing the function of effector T cells and enhancing the anti⁃tumor immune activity of macrophages. 

"> colorectal cancer, Modified Sijunzi Decoction, single?cell sequencing, tumor microen? vironment