The invention discloses a kit for amplifying a Her2 (Human epidermal growth factor receptor-2) gene in human peripheral blood circulating tumor DNA (Deoxyribonucleic Acid). By adopting component setting of the kit and a result reading scheme, a detection process is simple and convenient and the operability is strong. A detection result is reliable and has good specificity; meanwhile, a real-time fluorescence PCR (Polymerase Chain Reaction) technology is used for detecting an amplification level of the Her2 gene in a breast cancer tissue specimen through calculating a deltaCt value; the kit can be used for a plurality of research fields including breast cancer auxiliary diagnosis carried out through detection of ctDNA of the blood, clinical application, prognosis and the like.