Objective To establish a transgenic breast cancer mouse model with human Her2 overexpression and to identify the mouse model. Methods The purified exogenous plasmid pMD18T-MMTV-huHER2-EGFP was constructed and injected into C57BL/6J mouse fertilized eggs by prokaryotic microinjection method. Then the embryos were transplanted into the fallopian tubes of pseudopregnant mice in estrus simultaneously, and the offspring mice were obtained. The genomic DNA of offspring mice was identified by PCR method. The expression of Her2 protein in the breast tissue of offspring mice was detected by Western blotting analysis. The pathological changes of breast tissue in transgenic mice were observed by histopathological section. Results Her2 transgenic mice were detected by PCR method. Western blotting analysis showed that, compared with wild-type mice, the expression of Her2 protein in the breast tissue of F2 generation positive mice was significantly higher. Histopathological sections showed that the breast tissue of F2 generation positive mice of 25 weeks old had an obvious carcinogenic tendency. Conclusion The transgenic breast cancer mouse model with human Her2 overexpression has been successfully established, with stable genetic and spontaneous formation of breast cancer. The biological characteristics and pathological changes of the model are similar to human breast cancer, indicating that it can be used as an animal model to study the development and progression of breast cancer.