There are two main methods to determine whether colon cancer patients have lung metastasis: first, clinical manifestations: if colon cancer patients have respiratory symptoms such as coughing, coughing sputum, difficulty in breathing, shortness of breath, etc., then they should be alert to whether there is lung metastasis. Second, lung CT examination: if colon cancer patients undergo lung CT examination, if metastatic lesions are found in the lung, especially multiple nodal lesions, enhanced scan lesion intensification, irregular shape of lesions and burr at the edges, which are consistent with imaging characteristics of cancerous lesions, at this time, we can initially judge whether colon cancer has lung metastasis. If whole body PET-CT scan is done, it can better determine whether the lung lesion is benign or malignant lesion. If it is a malignant lesion, combined with the medical history of colon cancer, it can be basically concluded that there is lung metastasis.