Objective Establishment of a mouse model of orthotopic lung cancer and lymph node metastasis to simulate lymph node metastasis during the occurrence and development of lung cancer and to study the immune cells in the microenvironment before lung cancer metastasis occurs. Methods Mouse Lewis lung cancer cells were cultured and then injected through the chest walls of mice to establish an orthotopic mouse model of lung cancer. Samples were taken at 7, 14, 21, and 28 days after tumor transplantation, and the changes in the orthotopically transplanted tumors, lymph node tissue structure, and B cells were observed by HE staining and immunohistochemistry. Results The orthotopic C57BL/6J mouse model of lung cancer was successfully constructed, and the mediastinal lymph nodes were collected. The changes in the germinal center, lymphatic vessels, and blood vessels within the lymph nodes as well as structural alterations of lymph nodes associated with tumor metastasis and infiltration of tumor cells were observed during the progression of lung cancer using HE staining. Immunohistochemistry showed an increase in the density of B cells in the lymph nodes of the model group. Conclusions The establishment of this model lays a foundation for the future study of immune cells in the microenvironment of lung cancer before lymph node metastasis occurs.