The present invention provides a mutated antibody of the fully humanized HER2 antibody GB235-019, wherein the amino acid sequence of the heavy chain variable region and the amino acid sequence of the light chain variable region of the mutated antibody are respectively SEQ ID NO: 10, SEQ ID NO: 2; SEQ ID NO: 11, SEQ ID NO: 2; or SEQ ID NO: 12, SEQ ID NO: 2. The mutated antibody has the ability to specifically bind to human HER2 antigen, similar to the GB235-019 antibody. They can also be used in combination with additional HER2 positive tumor therapeutic agents for treating HER2 positive tumor, weakly positive tumor or negative tumor.