Surgery is the first choice in the treatment of non-small cell lung cancer, but only for early stage patients. Radiotherapy predominates in the treatment of locally advanced non-small cell lung cancer. Only about one-third of patients diagnosed with lung cancer can be treated with surgery, and one-third of them are locally advanced patients. Therefore, radiotherapy should play a very important role in the treatment of locally advanced patients, and can also be used for postoperative treatment and palliative treatment of stage IV patients. With the improvement of radiotherapy equipment and technology, the efficacy of radiotherapy for tumors has been significantly improved. As a result, radiotherapy plays an important role in the treatment of lung cancer. Especially since the 1990s, with the application of computer technology, an emerging radiotherapy technique, three-dimensional conformal radiotherapy and intensity-modulated radiotherapy, has been born. It includes three-dimensional structure reconstruction of tumor, normal tissues and organs, radiotherapy planning, dose calculation, plan verification, radiotherapy implementation, quality assurance and quality control. It makes radiation therapy more precise and the radiation dose is more uniformly concentrated in the tumor area, so that the normal tissues around the tumor are exposed to the minimum amount. That is, the increase of tumor dose is implemented without increasing the normal tissue irradiation, thus improving the local control rate of tumor. 3DCRT is based on three-dimensional multifield irradiation, where each field is focused on the same point, the tumor center. With a radiotherapy planning system, these fields can be precisely designed to achieve a tumor-killing dose and avoid overdosing of normal tissue. However, 3DCRT is suitable for most tumors that are relatively regular in shape. For irregularly growing tumors, especially those that are closely adherent to vital organs or concave in shape, 3DCRT still does not fully meet the treatment requirements. In these cases, IMRT is the best choice, which is based on multi-wild irradiation, giving uneven doses to each field according to the tumor, and adjusting the dose intensity to achieve the requirements of conformal irradiation. However, due to the unbalanced development of radiotherapy technology and equipment in China, and the high cost of IMRT treatment, the clinical application of this technology is not yet widespread. It is believed that with the popularization of IMRT technology, more patients with non-small cell lung cancer will benefit.