Pemetrexed single-agent maintenance regimen means to maintain the patient’s current condition and avoid its continuous progression. Pemetrexed belongs to multi-target antifolate metabolism targeted therapy drugs, mainly used in the treatment of locally progressive, metastatic non-small cell lung cancer, can be a single drug or a combination of drugs, of which pemetrexed single agent maintenance therapy means only using pemetrexed drug therapy, so that the condition is stabilized at the present time, to avoid the condition from continuing to deteriorate. Pemetrexed can interfere with the replication process of cancer cells but can neutralize the normal metabolism of folic acid, so as to inhibit the growth and reproduction of tumors, which is especially suitable for the older patients, with relatively less side effects, and is not easy to vomiting, hair loss, nausea, bone marrow suppression and so on.