Abstract: An anti-Her2/CD3 bispecific antibody is specifically activated in a tumor microenvironment. The bispecific antibody can be chemically conjugated to a substrate that is highly expressed in a tumor environment and can be recognized and cut, as well as a masking moiety, in a chemical coupling manner. The antibody activity of the bispecific antibody in normal tissues is suppressed, but is activated in a tumor environment. In addition, the bispecific antibody also has a significantly reduced toxicity.