Low oxygen saturation of 90% in the advanced stage of lung cancer is mainly caused by reduced lung function. After lung cancer patients enter the advanced stage, cancer cells have already invaded the whole lung, which will affect the lung function of the patients, leading to function decline or even failure, causing problems such as hypoxemia and respiratory failure, and thus oxygen saturation lower than 90% will occur. When oxygen saturation is lower than 90% in lung cancer patients, first of all, oxygen support therapy is needed so that oxygen saturation can be raised to above 90%; if the situation is serious, it is also necessary to use respiratory machine for assisted ventilation therapy. During the treatment period, according to the patient’s condition, radiotherapy, chemotherapy, targeted therapy and other treatments may also be needed.