Based on the obtained anti-CD20 nanobodies, we further used a genetic engineering method to construct the bispecific nanobody anti-CD20/CD3 BsNb by fusing the anti-CD20 VHH gene with a well-verified anti-human CD3 VHH, and the binding activity and tumor cell killing effect of the anti-CD20/CD3 BsNb were identified by an in vitro test. This evidence concerns the gene MS4A1 and neoplasm.