Objective Using the concept and method of allostatic load (AL) to evaluate aging and the effectiveness of Zuogui Pill intervention in aging. Methods Natural aging rats were tested at the ages of 2, 5, 8, 14, and 18 months, and were divided into an elderly control group, a low-dose group of Zuogui Pill, and a high-dose group of Zuogui Pill. Intervention with Zuogui Pill for 3 months. Blood samples were taken from the tail of rats of each month and group, and the number of T lymphocytes and apoptosis rate were measured by flow cytometry. Low-density lipoprotein cholesterol (LDL-c), High-density lipoprotein cholesterol (HDL-c), triglycerides (TG), total cholesterol (tCHO), free fatty acids (FFA), 25 hydroxyvitamin D (25-OHD), corticosterone (CORT), C-reactive protein (CRP), Interleukin-6 (IL-6) in rat serum were detected. By identifying the collinearity between indicators and professional considerations, LDL-c, tCHO, HDL-c, FFA, TG, CORT, IL-6, CRP, 25-OHD, CD3+ T cell count, and CD3+ T cell apoptosis rate were included for AL scoring. The threshold for each indicator was established on data from 5-month-old rats, and the score was 1 point below or/and above the threshold. Results The serum LDL-c, TG, tCHO, 25-OHD, CRP, and IL-6 of rats showed significant changes with age, but the change patterns were different. The CD3+ T lymphocyte count significantly decreased with age (P < 0.01), while the apoptosis rates of CD3+, CD4+, and CD8+ T lymphocytes significantly increased with age (P < 0.01). Zuogui Pill can significantly increase the serum CORT level in elderly rats (P < 0.01) and reduce the apoptosis rate of CD8+ T lymphocytes (P < 0.05). The AL score began to increase at 5 months of age and reached its peak at 18 months of age. Conclusion AL can better characterize the aging process compared to a single indicator. Zuogui Pill can improve the stress response ability of aging rats and alleviate their immune aging.