Background T cell immunoglobulin-3(Tim-3) is an immune checkpoint molecule; Tim-3 antibody is suitable for treating malignant renal tumours. However, Tim-3 antibody drugs are expensive, which limits their application. To overcome the disadvantages of expensive immunotherapeutic drugs, Lactococcus lactis was used as the host bacteria to express Tim-3 single-chain antibody in the intestine, and its promotion of the mouse immune system and inhibitory effects on the transplanted tumour of kidney cancer in mice were tested. Methods Molecular cloning technology was used to construct plasmids pLAN-CTB-Tim3scFv and pLAN-Tim3scFv, which were transformed into Lactococcus lactis. The expression of the transformed bacteria was analysed using western blotting, and the immune activity of secreted proteins of the transformed bacteria was detected using ELISA in vitro. A subcutaneous transplanted tumour model of renal adenocarcinoma was constructed in RAG mice, and the promoting effect of transforming bacteria on the activation of mouse spleen lymphocytes, and its inhibitory effect on transplanted tumours in mice was analysed. Results (1) Transformed Lactococcus lactis NZ -CTB-Tim3scFv and NZ -Tim3scFv, which secrete CTB-Tim3scFv and Tim3scFv single-chain antibodies, were successfully constructed. (2) CTB-Tim3scFv secreted by NZ-CTB-Tim3scFv transformed bacteria showed immunological activity. (3) Compared with the NZ-Tim3scFv and NZ-Vector groups, the characteristics of the subgroups of splenic lymphocytes in the NZ-CTB-Tim3scFv group had a higher proportion of CD3+CD4+, CD3+CD8a+, and CD3+CD69+ cells. Ki67 and CD31 expression in the NZ-CTB-Tim3scFv group was significantly reduced. The tumour volume of the NZ-CTB-Tim3scFv group increased the least, and was statistically different from that of the other two groups. Conclusions The Tim-3 single-chain antibody gene was successfully constructed and transformed in Lactococcus lactis. After feeding mice NZ-CTB-Tim3scFv transforming Lactobacillus, the CTB-Tim3scFv secreted by the transforming Lactobacillus promoted the proliferation and activation of spleen lymphocytes and inhibited volume growth, cell proliferation, and angiogenesis of the tumour in mice. In summary, apply transgenic lactobacillus secreting CTB-Tim-3scFv, to perform its role in anti-tumor immunotherapy through oral approach, is low cost and convenient. It is expected to become a new way of immunotherapy for renal cell carcinoma.