To explore the mechanism of Pi (Spleen)-deficiency-induced functional diarrhea (FD) model rats treated by Shenling Baizhu Powder (, SBP). Thirty male Sprague-Dawley rats were randomly divided into 5 groups including control, model, low-, medium-, and high-dose SBP groups (SBPLDG, SBPMDG, SBPHDG), 6 rats in each group, respectively. Pi-deficiency-induced FD rats model was developed through Radix et Rhizoma Rhei gavage for 7 days. After modeling, the rats were treated with 3 doses of SBP [0.93, 1.86, and 3.72 g/(kg·d)], and the rats in the control and model groups were given pure water for 7 days. The diarrhea index was calculated. On the 7th and 14th days, the traveled distance of rat was measured by the open field test. Serum D-xylose content was determined by the phloroglucinol method and interleukin (IL)-10 and IL-17 levels were measured using an enzyme-linked immunosorbent assay kit. The content of Treg cells was determined by flow cytometry. Compared with the control group, the diarrhea index and IL-17 level in the model group were significantly higher and the total exercise distance and D-xylose content significantly decreased (P>0.05). The expression of IL-10 in the SBPHDG group was significantly up-regulated, and serum D-xylose level and Treg cells increased significantly compared with the model group (P>0.05). High-dose SBP exhibited ameliorating effects against Pi-deficiency induced FD, which might be attributed to its modulations on intestinal absorption function as well as adaptive immunity in mesenteric lymph nodes of rat.