Objective To investigate the effect of Astragalus injection combined with Imipenem and Cilastatin Sodium on severe infection in the elderly. Methods According to the random table method 103 cases of elderly patients with severe infection selected as the subjects were divided into an observation group (54 cases) and a control group (49 cases). The patients in the observation group were treated with Astragalus injection combined with Imipenem and Cilastatin Sodium, while those in the control group were treated with only Imipenem and Cilastatin Sodium. The course of treatment in both groups was 14 days. Results The total effective rate of the observation group was higher than that of the control group (P < 0.05). The differences of CD3+ T lymphocytes, CD4+ T lymphocytes and CD4+/CD8+ ratio after treatment in the observation group were bigger than those in the control group (P < 0.05). The C-reactive protein, procalcitonin and WBC after treatment in the observation group were lower than those in the control group (P < 0.05). The morbidity of MODS in the observation group was significantly lower than that in the control group (P < 0.05). The time of intestinal function recovery in the observation group was shorter than that in the control group (P < 0.05). There was no significant difference in mortality between the observation group and the control group (P > 0.05). The adverse reaction rate of the observation group was lower than that of the control group (P < 0.05). Conclusions Astragalus injection combined with Imipenem and Cilastatin Sodium is effective in the treatment of elderly patients with severe infection.