Objective To explore the inhibiting effect of Astragalus membranaceus on the growth of renal cell carcinoma by promoting the activity of follicular helper T cells (Tfh cells). Methods A mouse model of renal cell carcinoma was established in 56 BALB/c mice, and then they were evenly divided into Astragalus membranaceus treatment group and control group. The mice in the Astragalus membranaceus treatment group were given 0.5 mg/g Astragalus membranaceus extract by tube feeding every day, while the mice in the control group were given the same volume of purified water every day. Three mice were sacrificed on days 0, 9, 12, 15, 18 and 21 respectively after modeling in both groups, the effect of Astragalus membranaceus extract on the growth of renal cell carcinoma was evaluated by measuring the tumor volume, and the Tfh cell proportion in tumor tissue was analyzed by flow cytometry. The remaining 10 mice were sacrificed on day 21 after modeling in both groups, the proportions of CD8⁺ T cells and Tfh cells were detected by flow cytometry, and the effect of Astragalus membranaceus extract on Tfh cells was explored by detecting the expression of cytokines. Results Compared with the control group, the volume of tumor in the Astragalus membranaceus treatment group was significantly smaller on days 18 and 21 (P<0.05), accompanied by an increase in Tfh tumor infiltration (P<0.05). The mRNA expression level of interleukin 21 (IL-21) in Tfh cells of the Astragalus membranaceus treatment group was significantly higher than that of the control group on day 21 (P<0.05), and the proportion of tumor-infiltrating CD8⁺ T cells was positively correlated with the proportion of tumor-infiltrating Tfh cells (r²=0.700, P=0.003) and the mRNA expression level of IL-21 in Tfh cells (r²=0.673, P=0.004). Conclusion Astragalus membranaceus can slow down the growth of renal cell carcinoma in mice, and may exert anti-tumor immune effects through Tfh cells.