Objective To study the effect of parenteral nutrition combined with chemotherapy on immune function in patients with digestive tract malignant tumor. Methods One hundred patients with digestive tract malignant tumor were selected, and they were divided into the observation group and the control group by random digits table method with 50 cases each. The patients in control group during chemotherapy did not receive special treatment, and the patients in observation group were given parenteral nutrition support according to the gastrointestinal function during chemotherapy. The nutrition index, immune function index and T lymphocyte subsets after treatment were observed. Results The transferrin, prealbumin, IgA, CD4+and CD4+/CD8+levels after treatment in observation group were significantly higher than those in control group: (2.41±0.53) g/L vs. (2.15±0.57) g/L, (0.28±0.07) g/L vs. (0.20±0.08) g/L, (3.25±1.19) g/L vs. (2.85±1.01) g/L, 0.403±0.065 vs. 0.323±0.083 and 2.15±1.02 vs. 1.35±0.73, while the IgM in observation group was significantly lower than that in control group: (1.02 ± 0.35) g/L vs. (1.48±0.78) g/L, and there were statistical differences ( P<0.05). There were no statistical differences in body weight, albumin, IgG, and CD8+between 2 groups (P>0.05). Conclusion Parenteral nutrition combined with chemotherapy can improve the immune function in patients with digestive tract malignant tumor, and provide a theoretical basis for the treatment of parenteral nutrition combination with chemotherapy.