Invasive lung adenocarcinoma stage 3a belongs to the middle and advanced stage of lung cancer, and the overall prognosis of patients is poorer and more serious. Lung adenocarcinoma is a kind of malignant tumor originated from the epithelium of bronchial mucosa. Invasive lung adenocarcinoma stage 3a belongs to the middle and advanced stage of lung cancer, which suggests that the patient’s tumor primary foci are large or invade the adjacent important organs, and the tumor foci have already appeared mediastinal lymph node metastasis on the same side of the tumor foci, but there is no distant metastasis manifestation. Specific evaluation criteria should follow the guidance of oncologists and pathologists. The treatment of invasive lung adenocarcinoma 3a can be surgery + adjuvant chemotherapy or radical radiotherapy, and targeted immunotherapy can also be considered. However, the overall prognosis is poor, with a five-year survival rate of 15%. It is recommended that patients with invasive lung adenocarcinoma stage 3a should go to regular hospitals as early as possible, follow the standardized diagnosis and treatment advice of specialists, and have regular follow-up. At the same time, keep a good attitude and healthy diet in daily life to promote the recovery of the body, improve the quality of life and prolong the survival time of patients.