The most common side effects of methotrexate include gastrointestinal reactions, such as stomatitis, lip ulcers, pharyngitis, nausea, vomiting, gastritis and diarrhea, and long-term use may also lead to white blood cell reduction, bone marrow suppression and mucositis. Methotrexate is an anti-folate antitumor drug, mainly through the inhibition of dihydrofolate reductase to prevent the synthesis of tumor cells, inhibit the growth and reproduction of tumor cells, reduce the inflammatory response caused by immunity, and also has the effect of immune suppression, so it has a good therapeutic effect on rheumatic diseases and tumors, but the dosage is not the same. Methotrexate should be taken once a week for rheumatologic diseases, and the maximum dose should not exceed four tablets. The blood and liver functions should be reviewed regularly to avoid bone marrow suppression and serious infections.