The invention relates to a mouse model with lung metastasis of gastric cancer and an establishment method thereof, and belongs to the technical field of experimental animals. According to the mouse model and the establishment method thereof, BGC-823 and MKN-45 gastric cancer cells are cultured in vitro, and resuspended to a proper concentration with sterile PBS when the cell viability is strong. After the cells are cultured inside the body of immunodeficient NUDE and SCID mice inoculated in immunodeficience through the caudal vein, the mouse model with lung metastasis of gastric cancer is successfully obtained by the identifications including the statistics of surface lung nodules, HE staining and IHC staining. According to the mouse model establishment, needed experimental conditions and operation are simple and convenient, lung metastasis lesions after the experiment are obvious, metastasis efficiency is high, and mice with metastatic lesions have moderate survival cycles. In the evaluation and statistics of the metastasis results, the macroscopic counting of the lung nodules is improved into the microscopic counting of the IHC staining positive cells, thereby obtaining more objective and accurate results. The animal model of tumor metastasis may be widely used in scientific research and teaching.