The stage of lung cancer cannot be determined simply by the size of the tumor, but also needs to be judged in combination with the presence of lymph nodes and distant metastasis. When there is a tumor in the lung, first of all, we have to judge whether the tumor is benign or malignant, and if it is malignant, it needs to be combined with the presence of lymph node metastasis and distant metastasis to comprehensively evaluate the tumor staging. At present, China’s lung cancer staging adopts TNM staging, with t indicating the size and scope of the primary tumor, N indicating whether there is infiltration and metastasis of regional lymph nodes, and M indicating distant metastasis. T2a indicates that the maximum diameter of the tumor is between 3cm-4cm. The clinical stages including T2a were stage IB, T2aN0M0; stage IIB, T2aN1M0; stage IIIA, T2a to bN2M0; stage IIIB, T2a to bN3M0; stage IVA, any T, any N, M1a, any T, any N, M1b; stage IVB: any T, any N, M1c. Therefore, it can be preliminarily judged that the lung cancer stage of a 3 to 4 cm tumor on the lung can be stage IB, stage IIB, stage IIIA, stage IIIB, stage IVA or stage IVB. Lung cancer patients should go to the hospital for examination in time and be treated actively under the guidance of doctors.