Objective Using different concentrations of Coxsackievirus B3 (CVB3) to infect young SD rats. To investigate the distribution of coxsackievirus B3 (CVB3) in rat tissues and the immune response and inflammatory factors, to clarify the immunopathological mechanism of viral infection and provide an experimental basis for drug screening and efficacy evaluation. Methods Young SD rats (7 days old) were injected intraperitoneally with different doses of CVB3 (TCID₅₀=10^-3.34 /100 μL) and the proportions of lymphocyte subsets (CD4⁺, CD8⁺ ) in whole blood at days 4 and 8 were detected by flow cytometry. The CVB3 loads in the heart, liver, spleen, brain, kidney, and gastrointestinal tissues were detected by real-time fluorescence quantitative polymerase chain reaction, TNF-α and IFN-γ levels were detected by enzyme-linked immunosorbent assay, and histomorphologic changes were observed by hematoxylin and eosin staining. Results Different doses of CVB3 caused different degrees of diarrhea and decreased body mass in young rats. CVB3 was mainly distributed in the stomach, small intestine, large intestine, and stools, with the highest load in the large intestine and stools. The stock solution group (TCID₅₀=10^-3.34 /100 μL) increased the proportion of CD8⁺ T cells in the whole blood in young rats and decreased the CD4⁺ /CD8⁺ ratio (P<0.05, P<0.01).Compared with the nomal group high TNF-α and low IFN-γ expression were observed in the large intestine of young rats in the concentrate group (P<0.05, P<0.01), and submucosal edema and inflammatory cell infiltration were observed in the large intestine (cecum and rectum). There were no significant differences in the proportion of lymphocyte subsets, TNF-α and IFN-γ levels, and morphological changes in whole blood of young rats in the group 10^-1, 10^-2, and 10^-3 (P>0.05). Conclusions Different doses of CVB3 can induce infections in young SD rats. CVB3 (TCID₅₀ = 10^-3.34 /100 μL) causes pathological changes in the large intestine (cecum and rectum) in young rats, and high virus replication can increase levels of inflammatory factors and cause an imbalance of immune cells. CVB3 may have a unique pathogenic mechanism in young rats, providing a theoretical basis for developing evaluation strategies for drugs against CVB3 virus infections.